View source for British anti-invasion preparations of the Second World War

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{{Use British English|date=May 2012}}
{{Use dmy dates|date=November 2020}}
[[File:British beach defence 1940.jpg|thumb|A British soldier on a [[beach]] in [[Southern England]], 7 October [[1940]].]]
[[File:Dated embrasure (detail).JPG|thumb|right|Detail from a pillbox [[embrasure]].]]
'''British anti-invasion preparations of the Second World War''' entailed a large-scale division of [[Military history of the United Kingdom during World War II|military]] and civilian [[mobilisation]] in response to the threat of invasion ([[Operation Sea Lion]]) by [[Nazi Germany#World War II|German armed forces in 1940 and 1941]]. The [[British Army]] needed to recover from the [[Battle of Dunkirk|defeat]] of the [[British Expeditionary Force (World War II)|British Expeditionary Force]] in France, and 1.5 million men were enrolled as part-time soldiers in the [[Home Guard (United Kingdom)|Home Guard]]. The rapid construction of [[field fortification]]s transformed much of the United Kingdom, especially [[southern England]], into a prepared battlefield. Sea Lion was never taken beyond the preliminary assembly of forces. Today, little remains of Britain's anti-invasion preparations, although reinforced concrete structures such as [[Pillbox (military)|pillboxes]] and anti-tank cubes can still be commonly found, particularly in the coastal counties.<ref>{{Cite web |title=World War 2 |url=http://harwichanddovercourt.com/world-war-2.html |access-date=2023-01-12 |website=A PICTORIAL POSTCARD HISTORY OF HARWICH, DOVERCOURT AND PARKESTON. |language=en}}</ref>
== Political and military background ==
On 1 September 1939, [[Polish September Campaign|Germany invaded Poland]]; two days later, Britain and France [[declaration of war|declared war]] on [[Nazi Germany|Germany]], launching the [[Second World War]]. Within three weeks, the [[Red Army]] of the Soviet Union [[Soviet invasion of Poland|invaded]] the [[Kresy|eastern regions of Poland]] in fulfilment of the secret [[Molotov–Ribbentrop Pact]] with Germany. A [[British Expeditionary Force (World War II)|British Expeditionary Force]] (BEF) was sent to the Franco-Belgian border, but Britain and France did not take any direct action in support of the Poles. By 1 October, Poland had been completely overrun.{{sfn|Ray|2000|pp=46–48}} There was little fighting over the months that followed. In a period known as the [[Phoney War]], soldiers on both sides trained for war and the French and British constructed and manned defences on the eastern borders of France.{{sfn|Ray|2000|pp=49–51}}
However, the [[Chamberlain war ministry|British War Cabinet]] became concerned about exaggerated intelligence reports, aided by German [[disinformation]], of large [[airborne forces]] which could be launched against Britain. At the insistence of [[Winston Churchill]], then the [[First Lord of the Admiralty]], a request was made that the [[Commander-in-Chief, Home Forces]], General Sir [[Walter Kirke]], should prepare a plan to repel a large-scale invasion. Kirke presented his plan on 15 November 1939, known as "Plan Julius Caesar" or "Plan J-C" because of the [[Code word (communication)|code word]] "Julius" which would be used for a likely invasion and "Caesar" for an imminent invasion. Kirke, whose main responsibility was to reinforce the BEF in France, had very limited resources available, with six poorly trained and equipped [[Territorial Army (United Kingdom)|Territorial Army]] divisions in England, two in Scotland and three more in [[military reserve|reserve]]. With France still a powerful ally, Kirke believed that the eastern coasts of England and Scotland were the most vulnerable, with ports and airfields given priority.{{sfn|Barclay |2013|loc= Chapter 2 Complacency: to May 1940}}
On 9 April 1940, [[Operation Weserubung|Germany invaded Denmark and Norway]].<ref>[http://avalon.law.yale.edu/imt/juddenma.asp War crimes trial judgement on the invasion of Norway], via the Avalon Project – accessed 14 January 2008</ref> This operation preempted Britain's own plans to invade Norway. Denmark surrendered immediately, and, after a short-lived attempt by the British to make a stand in the northern part of the country, Norway also fell. The invasion of Norway was a combined forces operation in which the German war machine projected its power across the sea; this German success would come to be seen by the British as a dire portent.{{sfn|MacKenzie|1995|p=20}} On 7 and 8 May 1940, the [[Norway Debate]] in the [[British House of Commons]] revealed intense dissatisfaction with, and some outright hostility toward, the government of Prime Minister [[Neville Chamberlain]]. Two days later Chamberlain resigned and was succeeded by Churchill.{{sfn|Ray|2000|p=61}}
On 10 May 1940, [[Battle of France|Germany invaded France]]. By that time, the BEF consisted of 10 [[infantry]] divisions in three [[corps]], a [[tank]] brigade and a [[Royal Air Force]] detachment of around 500 aircraft.{{sfn|Ray|2000|p=53}} The BEF and the best French forces were pinned by the German attack into Belgium and the Netherlands,{{sfn|Ray|2000|p=63}} but were then outflanked by the main attack that came behind them through the [[Ardennes]] Forest by highly mobile ''[[Panzer]]'' divisions of the ''[[Wehrmacht]]'', overrunning any defences that could be improvised in their path. In fierce fighting, most of the BEF were able to avoid being surrounded by withdrawing to a small area around the French port of [[Dunkirk]].{{sfn|Ray|2000|pp=64–67}} With the Germans now on the coast of France, it became evident that an urgent reassessment needed to be given to the possibility of having to resist an attempted invasion of Britain by German forces.{{sfn|Barclay |2013|loc= Chapter 3 The May Panic}}
==British armed forces==
===British Army===
{{main|Operation Sea Lion order of battle}}
[[File:British prisoners at Dunkerque, France.jpg|thumb|right|upright|Captured British and French soldiers help one another on the staircase up to the cliff at [[Veules-les-Roses]], June 1940]]
The evacuation of [[British Army|British]] and [[French Army|French]] forces ([[Operation Dynamo]]) began on 26 May with air cover provided by the Royal Air Force at heavy cost. Over the following ten days, 338,226 French and British soldiers were [[Dunkirk evacuation|evacuated to Britain]]. Most of the personnel were brought back to Britain, but many of the army's vehicles, tanks, guns, ammunition and heavy equipment and the RAF's ground equipment and stores were left behind in France.<ref>{{cite news | title=1940: Dunkirk rescue is over&nbsp;– Churchill defiant |work=BBC | url=http://news.bbc.co.uk/onthisday/hi/dates/stories/june/4/newsid_3500000/3500865.stm | access-date=28 July 2006 |date=4 June 1940}}</ref> Some soldiers even returned without their rifles. A further 215,000 were evacuated from ports south of the Channel in the more organised [[Operation Aerial]] during June.<ref>{{cite encyclopedia | title=Operation Aerial, the evacuation from north western France, 15–25 June 1940 | encyclopedia=Military History Encyclopedia on the Web | url=http://www.historyofwar.org/articles/operation_aerial.html | access-date=21 December 2010 }}</ref>
In June 1940 the [[British Army during the Second World War|British Army]] had 22 infantry divisions and one armoured division. The infantry divisions were, on average, at half strength, and had only one-sixth of their normal artillery.{{sfn|Lowry|2004|p=11}} Over 600 medium guns, both 18/25 and [[Ordnance QF 25-pounder|25 pounder]]s, and 280 howitzers were available, with a further one hundred 25-pounders manufactured in June. In addition, over 300 [[BL 4.5-inch Medium Field Gun|4.5-inch]] howitzers{{spaced en dash}}900 were modified in 1940 alone{{spaced en dash}}and some [[BL 60-pounder gun|60-pounder]] howitzers and their modified 4.5-inch version as well as antiquated examples of the [[BL 6-inch gun Mk XIX|6-inch]] howitzer were recovered from reserve after the loss of current models in France.<ref>{{cite web|title=British Equipment Losses at Dunkirk|url=http://www.wwiiequipment.com/index.php?option=com_content&view=article&id=125:british-equipment-losses-at-dunkirk-and-the-situation-post-dunkirk&catid=50:other-articles&Itemid=61 |author=Boyd, David |work=British Equipment of the Second World War |access-date=30 March 2021}}</ref> These were augmented with several hundred additional [[75 mm Gun M1917|75-mm M1917 guns]] and their ammunition from the US. Some sources also state the British army was lacking in transport (just over 2,000 [[Universal Carrier|carriers]] were available, rising to over 3,000 by the end of July). There was a critical shortage of ammunition such that little could be spared for training.{{sfn|MacKenzie|1995|p=52}}
In contrast, records show that the British possessed over 290 million rounds of .303 ammunition of various types on 7 June, rising to over 400 million in August. [[VII Corps (United Kingdom)|VII Corps]] was formed to control the Home Forces' general reserve, and included the [[1st Armoured Division (United Kingdom)|1st Armoured Division]]. In a reorganisation in July, the divisions with some degree of mobility were placed behind the "coastal crust" of defended beach areas from [[The Wash]] to [[Newhaven, East Sussex|Newhaven in Sussex]]. The General Headquarters Reserve was expanded to two corps of the most capable units. VII Corps was based at [[Headley Court]] in Surrey to the south of London and comprised 1st Armoured and [[1st Canadian Division]]s with the [[1st Army Tank Brigade (United Kingdom)|1st Army Tank Brigade]]. [[IV Corps (United Kingdom)|IV Corps]] was based at [[Latimer House]] to the north of London and comprised [[2nd Armoured Division (United Kingdom)|2nd Armoured]], [[42nd (East Lancashire) Infantry Division|42nd]] and [[43rd (Wessex) Infantry Division|43rd Infantry]] divisions.<ref>{{harvnb|Collier|1957|p=220}}</ref> VII Corps also included a brigade, which had been diverted to England when on its way to Egypt, from the [[2nd New Zealand Expeditionary Force]].<ref>{{harvnb|Stevens|1958|pp=27–28}}</ref><ref>{{harvnb|McClymont|1959|p=36}}</ref> Two infantry brigades and corps troops including artillery, engineers and medical personnel from the Australian [[6th Division (Australia)|6th Division]] were also deployed to the country between June 1940 and January 1941 as part of the [[Second Australian Imperial Force in the United Kingdom]].{{sfn|Long|1952|pp=306–307}}
The number of tanks in Britain increased rapidly between June and September 1940 (mid-September being the theoretical planned date for the launch of Operation Sea Lion) as follows:<ref>{{Cite journal |last=Forrester |first=Rochelle |date=2021-06-28 |title=Operation Sea Lion, the Luftwaffe, the Kanalkampf and the Battle of Britain - the Defence of Britain in1940 and Air Power in World War 2 |type=Preprint |access-date=2023-01-12 |website=SocArXiv |doi=10.31235/osf.io/fb7xw |s2cid=240943296 |url=https://osf.io/preprints/socarxiv/fb7xw/}}</ref>
{|class="wikitable"
!Date!!Light tanks!!Cruisers!!Infantry tanks
|-
|10 Jun 1940|| 292 ||0|| 74
|-
|1 Jul 1940|| 265||118||119
|-
|4 Aug 1940|| 336|| 173 || 189
|-
|('''''sent to'''''<br />'''''Egypt''''')|| (−52)||(−52)||(−50)
|-
|27 Aug 1940|| 295|| 138|| 185
|-
|15 Sept 1940 ||306  || 154 || 224
|}
These figures do not include training tanks or tanks under repair.
[[File:IWM-H-7331-Beaverette-Scotland-19410214.jpg|thumb|right|[[Standard Beaverette|Standard Mk II Beaverette]] light reconnaissance cars manned by members of the Home Guard in the Highlands of Scotland, 14 February 1941]]
The light tanks were mostly [[Light Tank Mk VI|MkVIB]] and the cruiser tanks were [[Cruiser Mk I|A9]] / [[Cruiser Mk II|A10]] / [[Cruiser Mk IV|A13]]. The infantry tanks included 27 obsolete [[Matilda Mk. I|Matilda MkIs]] but the rest were almost all the very capable [[Matilda II]].<ref>Appendix 7 to 13 of David Newbold`s "British planning and preparations to resist an invasion on land Sept 1939 to Sept 1940" British Library EThOS ID 241932</ref> The first [[Valentine tank|Valentine infantry tank]]s were delivered in May 1940 for trials and 109 had been built by the end of September.<ref>{{cite web |url=http://www.historyofwar.org/articles/weapons_valentine_infantry_tank_III.html |title= Infantry Tank Mk III – Valentine |last=Rickard |first=John |date=7 May 2015 |website=www.historyofwar.org |access-date=14 June 2020 }}</ref> In the immediate aftermath of Dunkirk some tank regiments, such as the [[4th/7th Royal Dragoon Guards]], were expected to go into action as infantry armed with little more than rifles and light machine guns. In June 1940 the regiment received the [[Beaverette]], an improvised armoured car developed by order of the [[Minister of Aircraft Production]] [[Lord Beaverbrook]], and former holiday coaches for use as personnel carriers. It did not receive tanks until April 1941 and then the problematic [[Covenanter tank|Covenanter]].{{sfn|Thompson|2009|p=221}}
Churchill stated "in the last half of September we were able to bring into action on the south coast front sixteen divisions of high quality of which three were armoured divisions or their equivalent in brigades".{{sfn|Churchill|1978|p=344}} It is significant that the British Government felt sufficiently confident in Britain's ability to repel an invasion (and in its tank production factories) that it sent 154 tanks (52 light, 52 cruiser and 50 infantry) to Egypt in mid-August. At this time, Britain's factories were almost matching Germany's output in tanks and, by 1941, they would surpass them.{{sfn|Edgerton|2012|p=64}}
=== Home Guard ===
{{Main|Home Guard (United Kingdom)}}
On 14 May 1940, Secretary of State for War [[Anthony Eden]] announced the creation of the Local Defence Volunteers (LDV){{spaced en dash}}later to become known as the Home Guard. Far more men volunteered than the government expected and by the end of June, there were nearly 1.5&nbsp;million volunteers. There were plenty of personnel for the defence of the country, but there were no uniforms (a simple armband had to suffice) and equipment was in critically short supply. At first, the Home Guard was armed with guns in private ownership, knives or bayonets fastened to poles, [[Molotov cocktail]]s and improvised [[flamethrower]]s.<ref>{{cite web | title=Nuttall Flame Thrower | work=The History of Wolverhampton&nbsp;– The City and its People | url=http://www.wolverhamptonhistory.org.uk/people/at_war/ww2/fighting3 | access-date=28 July 2006 | archive-url=https://web.archive.org/web/20140811125138/http://www.wolverhamptonhistory.org.uk/people/at_war/ww2/fighting3 | archive-date=11 August 2014 }}</ref><ref>{{cite web | title=Colour movie of Home Guard training including a Harvey flamethrower | work=Britons at War | url=http://www.nationalmediamuseum.org.uk/nmem/britonsatwar/detail.asp?topicnum=1&id=37 | access-date=29 March 2012}}</ref>
[[File:British Home Guard Improvised Weapons.JPG|thumb|left|Home Guard improvised weapons]]
By July 1940 the situation had improved radically as all volunteers received uniforms and a modicum of training. 500,000 modern [[M1917 Enfield Rifle]]s, 25,000 [[M1918 Browning Automatic Rifle]]s and millions of rounds of ammunition were bought from the reserve stock of the U.S. armed forces, and rushed by special trains directly to Home Guard units.<ref name="evans68">{{harvnb|Evans|2004|p=68}}</ref> New weapons were developed that could be produced cheaply without consuming materials that were needed to produce armaments for the regular units. An early example was the [[No. 76 Special Incendiary Grenade]], a glass bottle filled with highly flammable material of which more than six million were made.{{sfn|MacKenzie|1995|p=92}}
The [[sticky bomb]] was a glass flask filled with [[nitroglycerin]] and given an adhesive coating allowing it to be glued to a passing vehicle. In theory, it could be thrown, but in practice it would most likely need to be placed{{spaced en dash}}thumped against the target with sufficient force to stick{{spaced en dash}}requiring courage and good fortune to be used effectively. An order for one million sticky bombs was placed in June 1940, but various problems delayed their distribution in large numbers until early 1941, and it is likely that fewer than 250,000 were produced.<ref>Anti-tank measures Sticky Bomb adoption and production&nbsp;– [http://www.nationalarchives.gov.uk/catalogue/ExternalRequest.asp?RequestReference=WO185/1 WO 185/1]. ''The Catalogue'', [[The National Archives (United Kingdom)|The National Archives]]</ref>
A measure of mobility was provided by bicycles, motorcycles, private vehicles and horses. A few units were equipped with armoured cars, some of which were of standard design, but many were improvised locally from commercially available vehicles by the attachment of steel plates.{{sfn|Mace|2001|p=92}}  By 1941 the Home Guard had been issued with a series of "sub-artillery", a term used to describe hastily produced and unconventional anti-tank or infantry support weapons, including the [[Blacker Bombard]] (an anti-tank [[spigot mortar]]), the [[Northover Projector]] (a black-powder mortar), and the [[Smith Gun]] (a small artillery gun that could be towed by a private motorcar).{{sfn|Clarke|2010|p=157}}
===Royal Air Force===
{{Main|Battle of Britain}}
[[File:Chain home coverage.jpg|thumb|Chain Home radar coverage. High-level coverage in September 1939 (dashed lines) and September 1940 (solid lines).]]
In mid-1940, the principal concern of the Royal Air Force, together with elements of the [[Fleet Air Arm]], was to contest the control of British airspace with the German [[Luftwaffe]]. For the Germans, achieving at least local [[air superiority]] was an essential prerequisite to any invasion and might even break British morale, forcing them to [[Suing for peace|sue for peace]].{{sfn|Ray|2000|p=83}}
If the German air force had prevailed and attempted a landing, a much-reduced Royal Air Force would have been obliged to operate from airfields well away from the southeast of England. Any airfield that was in danger of being captured would have been made inoperable and there were plans to remove all portable equipment from vulnerable [[radar]] bases and completely destroy anything that could not be moved.<ref>{{Cite book |last=Hernon |first=Ian |url=https://books.google.com/books?id=YQkTDQAAQBAJ&dq=Any+airfield+that+was+in+danger+of+being+captured+would+have+been+made+inoperable+and+there+were+plans+to+remove+all+portable+equipment+from+vulnerable+radar+bases+and+completely+destroy+anything+that+could+not+be+moved.&pg=PT260 |title=Fortress Britain: All the Invasions and Incursions since 1066 |date=2013-08-01 |publisher=The History Press |isbn=978-0-7524-9717-4 |language=en}}</ref>  Whatever was left of the RAF would have been committed to intercepting the invasion fleet in concert with the Royal Navy{{sfn|Parker|2000|p=309}}{{spaced en dash}}to fly in the presence of an enemy that enjoys air superiority is very dangerous. However, the RAF would have kept several advantages, such as being able to operate largely over friendly territory, as well as having the ability to fly for longer as, until the Germans were able to operate from airfields in England, ''Luftwaffe'' pilots would still have to fly significant distances to reach their operational area.<ref>{{Cite book |last=Hernon |first=Ian |url=https://books.google.com/books?id=YQkTDQAAQBAJ&dq=However%2C+the+RAF+would+have+kept+several+advantages%2C+such+as+being+able+to+operate+largely+over+friendly+territory%2C+as+well+as+having+the+ability+to+fly+for+longer+as%2C+until+the+Germans+were+able+to+operate+from+airfields+in+England%2C+Luftwaffe+pilots+would+still+have+to+fly+significant+distances+to+reach+their+operational+area.&pg=PT260 |title=Fortress Britain: All the Invasions and Incursions since 1066 |date=2013-08-01 |publisher=The History Press |isbn=978-0-7524-9717-4 |language=en}}</ref>
A contingency plan called [[Operation Banquet]] required all available aircraft to be committed to the defence. In the event of invasion almost anything that was not a fighter would be converted to a bomber{{spaced en dash}}student pilots, some in the very earliest stages of training, would use around 350 [[De Havilland Tiger Moth|Tiger Moth]] and [[Miles Magister|Magister]] trainers to drop {{convert|20|lb|abbr=on}} bombs from rudimentary bomb racks.{{sfn|Cox|1974|p=149}}
Shortly before the outbreak of the Second World War the [[Chain Home]] radar system began to be installed in the south of England, with three radar stations being operational by 1937.<ref>{{cite web|url=http://www.undergroundkent.co.uk/swingate_chain_home_station.htm |work=Undergroundkent.co.uk |title= Swingate Chain Home Station |access-date=16 April 2007 |archive-url=https://web.archive.org/web/20061129032733/http://www.undergroundkent.co.uk/swingate_chain_home_station.htm |archive-date=29 November 2006 }}</ref> Although the German High Command suspected that the British may have been developing these systems, [[Zeppelin]] detection and evaluation flights had proved inconclusive. As a result, the Germans underestimated the effectiveness of the expanding Chain Home radar system,{{sfn|Department of the Air Force|1962|loc=Chapter 1–3}} which became a vital piece of Britain's defensive capabilities during the [[Battle of Britain]].<ref>{{cite web |title=How Radar Gave Britain The Edge In The Battle Of Britain |url=https://www.iwm.org.uk/history/how-radar-gave-britain-the-edge-in-the-battle-of-britain |website=Imperial War Museums |access-date=31 March 2021 |language=en}}</ref><ref>{{cite web |title=RADAR – The Battle Winner? |url=https://www.rafmuseum.org.uk/research/online-exhibitions/history-of-the-battle-of-britain/radar-the-battle-winner/ |website=RAF Museum |access-date=31 March 2021}}</ref> By the start of the war, around 20 Chain Home stations had been built in the UK; to supplement these and detect aircraft at lower altitudes, the [[Chain Home Low]] was also being constructed.{{sfn|Hough|Richards|1990|p=51}}
===Royal Navy===
[[File:HMS Aurora 1942 IWM A 8158.jpg|thumb|right|The light cruiser [[HMS Aurora (12)|HMS ''Aurora'']] that bombarded Boulogne on 8 September 1940]]
Although much larger in size and with many more ships, the Royal Navy, unlike the [[Kriegsmarine]], had many commitments, including against Japan and guarding Scotland and Northern England. The Royal Navy could overwhelm any force that the German Navy could muster but would require time to get its forces in position since they were dispersed, partly because of these commitments and partly to reduce the risk of air attack. On 1 July 1940, one cruiser and 23 destroyers were committed to escort duties in the [[Western Approaches]], plus 12 destroyers and one cruiser on the [[River Tyne, England|Tyne]] and the [[aircraft carrier]] {{HMS|Argus|I49|3}}. More immediately available were ten destroyers at the south coast ports of [[Dover]] and [[Portsmouth]], a cruiser and three destroyers at [[Sheerness]] on the [[River Thames]], three cruisers and seven destroyers at the [[Humber]], nine destroyers at [[Harwich]], and two cruisers at [[Rosyth]]. The rest of the [[Home Fleet]]{{spaced en dash}}five battleships, three cruisers and nine destroyers{{spaced en dash}}was based far to the north at [[Scapa Flow]].<ref name="evans68" /> There were, in addition, many [[corvette]]s, [[minesweeper (ship)|minesweepers]], and other [[Coastal Forces of the Royal Navy|small vessels]].<ref>James, 2006, p. 39. Brian James notes that while the Germans had four minelayers in their western fleet, the British had 52 minesweepers and 16 minesweeping trawlers.</ref> By the end of July, a dozen additional destroyers were transferred from escort duties to the defence of the homeland, and more would join the Home Fleet shortly after.{{sfn|Evans|2004|p=69}}
At the end of August, the battleship {{HMS|Rodney|29|6}} was sent south to Rosyth for anti-invasion duties. She was joined on 13 September by her sister ship {{HMS|Nelson|28|6}}, the battlecruiser {{HMS|Hood|51|6}}, three anti-aircraft cruisers and a destroyer flotilla.<ref name="naval-history.net">{{cite web |url=http://www.naval-history.net/xDKWW2-4009-22SEP01.htm |title=Naval Events, 1–14 September 1940 |work=Naval history net |access-date=31 March 2021}}</ref> On 14 September, the old battleship {{HMS|Revenge|06|6}} was moved to [[Plymouth]], also specifically in case of invasion.<ref name= "Revenge">{{cite web|url=http://www.naval-history.net/xGM-Chrono-01BB-Revenge.htm |title=Service Histories of Royal Warships in World War 2 – HMS Revenge – Royal Sovereign-class 15in gun Battleship |last1=Mason |first1=Geoffrey B |date=10 April 2012 |website=Royal Navy and Naval History.net |access-date=26 January 2014}}</ref> In addition to these major units, by the beginning of September the Royal Navy had stationed along the south coast of England between Plymouth and Harwich, 4 light cruisers and 57 destroyers tasked with repelling any invasion attempt, a force many times larger than the ships that the Germans had available as naval escorts.<ref>{{harvnb|Hewitt|2008|p=163}}</ref>
==Field fortifications==
[[File:Coast Defence Battery - September 1940 Art.IWMARTLD838.jpg|thumb|British coastal artillery in September 1940, painting by [[Barnett Freedman]]]]
[[File:Allied Forces in the United Kingdom 1939-45 H5493.jpg|thumb|Engineers of the 1st Rifle Brigade (1st Polish Corps) constructing beach defences at Tentsmuir in Scotland. The concrete blocks were used as anti-tank obstacles.]]
{{main|British hardened field defences of World War II}}
The British engaged upon an extensive program of field fortification. On 27 May 1940 a Home Defence Executive was formed under [[Edmund Ironside, 1st Baron Ironside|General Sir Edmund Ironside]], Commander-in-Chief, Home Forces, to organise the defence of Britain.{{sfn|Wills|1985|p=9}} At first defence arrangements were largely static and focused on the coastline (the coastal crust) and, in a classic example of [[defence in depth]], on a series of inland anti-tank 'stop' lines.{{sfn|Atkin|2015|p=31}} The [[:Category:British World War II defensive lines|stop lines]] were designated command, corps and divisional according to their status and the unit assigned to man them.{{sfn|Collier|1957|p=129}} The longest and most heavily fortified was the General Headquarters anti-tank line, [[GHQ Line]]. This was a line of pill boxes and anti-tank trenches that ran from Bristol to the south of London before passing to the east of the capital and running northwards to York.{{Sfn|Bennett|1998|p=191}}  The GHQ line was intended to protect the capital and the industrial heartland of England.{{sfn|Atkin|2015|p=31}} Another major line was the [[Taunton Stop Line]], which defended against an advance from England's south-west peninsula.{{sfn|Foot|2006|p=13}} London and other major cities were ringed with inner and outer stop lines.{{Sfn|Storey|2020|p=210}}
Military thinking shifted rapidly. Given the lack of equipment and properly trained men, Ironside had little choice but to adopt a strategy of static warfare, but it was soon perceived that this would not be sufficient. Ironside has been criticised for having a siege mentality, but some consider this unfair, as he is believed to have understood the limits of the stop lines and never expected them to hold out indefinitely.{{sfn|Foot|2006|pp=12–13}}{{sfn|Churchill|1949|p=155}}
Churchill was not satisfied with Ironside's progress, especially with the creation of a mobile reserve. Anthony Eden, the Secretary of State for War, suggested that Ironside should be replaced by General [[Alan Brooke, 1st Viscount Alanbrooke|Alan Brooke]] (later Viscount Alanbrooke). On 17 July 1940 Churchill spent an afternoon with Brooke{{sfn|Alanbrooke|2001|loc=Entry 17 July 1940}} during which the general raised concerns about the defence of the country. Two days later Brooke was appointed to replace Ironside.{{refn|Churchill's account suggests that the afternoon meeting and Brooke's promotion occurred on the same day,{{sfn|Churchill|1949|pp=233–234}} but Brooke's diary entry indicates a two-day delay.|group="nb"}}{{sfn|Todman|2016|p=405}}
Brooke's appointment saw a change in focus away from Ironside's stop lines, with cement supplies limited Brooke ordered that its use be prioritised for beach defences and "nodal points".{{Sfn|Schofield|2009|p=144}}  The nodal points, also called anti-tank islands or fortress towns, were focal points of the [[hedgehog defence]] and expected to hold out for up to seven days or until relieved.{{Sfn|Hylton|2004|p=78}}
===Coastal crust===
{{See also|Dover Strait coastal guns}}
{{Multiple image|total_width=300
|image1=Inchgarvie.JPG
|alt1=
|caption1=[[Inchgarvie]] just below the [[Forth Bridge (railway)|Forth Bridge]]
|image2=Coast Seachlight, Freiston Shore.JPG
|alt2=
|caption2=Coastal searchlight emplacement
}}
[[File:Concertina wire.png|thumb|upright|Concertina wire]]
The areas most vulnerable to an invasion were the south and east coasts of England. In all, a total of 153 Emergency Coastal Batteries were constructed in 1940 in addition to the existing coastal artillery installations, to protect ports and likely landing places.<ref>{{harvnb|Schenk|1990|p=347}}</ref> They were fitted with whatever guns were available, which mainly came from naval vessels scrapped since the end of the First World War. These included 6&nbsp;inch (152&nbsp;mm), 5.5&nbsp;inch (140&nbsp;mm), 4.7&nbsp;inch (120&nbsp;mm) and 4&nbsp;inch (102&nbsp;mm) guns. Some had little ammunition, sometimes as few as ten rounds apiece. At Dover, two 14&nbsp;inch (356&nbsp;mm) guns known as [[Winnie (coastal battery)|Winnie]] and [[Pooh (coastal battery)|Pooh]] were employed.{{sfn|Evans|2004|p=59}} There were also a few land-based torpedo batteries.<ref>{{cite web| url=http://www.nci-frowardpoint.org.uk/sitehistory.htm | title=Froward Point Team, Kingswear, Devon&nbsp;– site history | work=National Coastwatch | access-date=19 February 2007| archive-url = https://web.archive.org/web/20061207203946/http://www.nci-frowardpoint.org.uk/sitehistory.htm| archive-date = 7 December 2006}}</ref>
[[File:Tank trap with graffiti - geograph.org.uk - 174639.jpg|thumb|Anti-tank concrete cube on the beach at [[Newburgh, Fife]]. It is carved with graffiti, including the words "HITLER'S GRAVEYARD."]]
Beaches were blocked with [[wire entanglement|entanglements of barbed wire]], usually in the form of three coils of [[concertina wire]] fixed by metal posts, or a simple fence of straight wires supported on waist-high posts.{{sfn|Ruddy|2003|p=24}} The wire would also demarcate extensive [[minefield]]s, with both anti-tank and anti-personnel mines on and behind the beaches. On many of the more remote beaches this combination of wire and mines represented the full extent of the passive defences.<ref>{{Cite web |title=World War Two |url=http://romneymarshhistory.com/ |access-date=2023-01-12 |website=History of Romney Marsh}}</ref>
Portions of [[Romney Marsh]], which was the planned invasion site of Operation Sea Lion, were flooded<ref>Gowdin & Ingrams, ''Romney Marsh'', p. 107.</ref> and there were plans to flood more of the Marsh if the invasion were to materialise.<ref>{{cite web
|title        = Improvisation Sir
|author       = Phil Sealey
|work         = WW2 People's War (BBC)
|url          = http://www.bbc.co.uk/ww2peopleswar/stories/83/a4967283.shtml
|access-date  = 3 November 2011
|archive-date = 20 July 2012
|archive-url  = https://archive.today/20120720220519/http://www.bbc.co.uk/ww2peopleswar/stories/83/a4967283.shtml
}}</ref>
Piers, ideal for landing troops, and situated in large numbers along the south coast of England, were disassembled, blocked or otherwise destroyed. Many piers were not repaired until the late 1940s or early 1950s.<ref>{{cite news| url=https://www.theguardian.com/uk_news/story/0,3604,953927,00.html | title= Arson fear as Brighton pier burns again |work=The Guardian |location=London | access-date=16 April 2007 | first=Jeevan | last=Vasagar | date=12 May 2003}}</ref>
Where a barrier to tanks was required, [[Admiralty scaffolding]] (also known as beach scaffolding or obstacle Z.1) was constructed. Essentially, this was a fence of scaffolding tubes {{convert|9|ft|m}} high and was placed at low water so that tanks could not get a good run at it.{{sfn|Ruddy|2003|p=25}} Admiralty scaffolding was deployed along hundreds of miles of vulnerable beaches.<ref>{{cite web| url=http://s134542708.websitehome.co.uk/pillboxes/html/beach_scaffolding_0.html| title=Beach scaffolding, Lunan bay, Angus| work=Pillbox UK, Photograph by Anne Burgess| access-date=22 June 2006| archive-url=https://web.archive.org/web/20100717132135/http://s134542708.websitehome.co.uk/pillboxes/html/beach_scaffolding_0.html| archive-date=17 July 2010}}</ref>
The beaches themselves were overlooked by [[British hardened field defences of World War II|pillboxes of various types]]. These were sometimes placed low down to get maximum advantage from [[enfilade and defilade|enfilading fire]], whereas others were placed high up making them much harder to capture. Searchlights were installed at the coast to illuminate the sea surface and the beaches for artillery fire.{{sfn|Ruddy|2003|p= 22}}<ref>{{cite web | url=http://s134542708.websitehome.co.uk/pillboxes/html/beach_defence_light.html | title=Beach Defence Light | work=Pillboxes UK | access-date=9 July 2006 | archive-url=https://web.archive.org/web/20070928004445/http://s134542708.websitehome.co.uk/pillboxes/html/beach_defence_light.html | archive-date=28 September 2007}}</ref><ref>{{cite web| url=http://www.users.globalnet.co.uk/~rwbarnes/defence/guest/casl-.htm | title=Restored Coastal Artillery Searchlight, Weymouth | access-date=16 July 2006}}</ref>
Many small islands and peninsulas were fortified to protect inlets and other strategic targets. In the [[Firth of Forth]] in east central Scotland, [[Inchgarvie]] was heavily fortified with several gun emplacements, which can still be seen. This provided invaluable defence from seaborne attacks on the Forth Bridge and [[Rosyth Dockyard]],<ref>{{cite web| url=http://www.scottish-places.info/features/featurefirst1302.html | title=Overview of Inchgarvie from Edinburgh University Geography Department's Gazetteer for Scotland | access-date=13 April 2007}}</ref> approximately a mile upstream from the bridge. Further out to sea, [[Inchmickery]], {{convert|1.6|mi|km}} north of Edinburgh, was similarly fortified. The remnants of gun emplacements on the coast to the north, in [[North Queensferry]], and south, in [[Dalmeny]], of Inchmickery also remain.<ref>{{cite web| url=http://local.live.com/default.aspx?v=2&cp=55.989455~-3.382531&style=h&lvl=19&tilt=-90&dir=0&alt=-1000&encType=1| title=Satellite link to gun emplacements on the south bank of the Firth of Forth | access-date=13 April 2007}}</ref>
===Lines and islands===
{{Multiple image|total_width=300|align=left
|image1=Anti-tank cubes, Tilford.JPG
|alt1=
|caption1=Anti-tank cubes
|image2=Anti-tank cylinder, Moor Park College.JPG
|alt2=
|caption2=Anti-tank cylinder
}}
The primary purpose of the stop lines and the anti-tank islands that followed was to hold up the enemy, slowing progress and restricting the route of an attack. The need to prevent tanks from breaking through was of key importance. Consequently, the defences generally ran along pre-existing barriers to tanks, such as rivers and canals; railway embankments and cuttings; thick woods; and other natural obstacles. Where possible, usually well-drained land was allowed to flood, making the ground too soft to support even tracked vehicles.{{sfn|Wills|1985|p=57}}
Thousands of miles of [[Anti-tank trench|anti-tank ditches]] were dug, usually by mechanical excavators, but occasionally by hand. They were typically {{convert|18|ft|m}} wide and {{convert|11|ft|m}} deep and could be either trapezoidal or triangular in section with the defended side being especially steep and [[revetment|revetted]] with whatever material was available.{{sfn|Ruddy|2003|p=29}}<ref>{{cite web| url=http://www.southsomersetmuseums.org.uk/heritage/chard-tankditch.htm| archive-url=https://web.archive.org/web/20061003054835/http://www.southsomersetmuseums.org.uk/heritage/chard-tankditch.htm| archive-date=3 October 2006| title=Location of anti-tank ditch | work=South Somerset Museums and Heritage Services | url-status=usurped| access-date=22 February 2007}} A rare extant example.</ref>
Elsewhere, anti-tank barriers were made of massive reinforced concrete obstacles, either cubic, pyramidal or cylindrical. The cubes generally came in two sizes: {{convert|5|or|3.5|ft|m}} high.{{sfn|Ruddy|2003|p=26}}<ref>{{cite web| url=http://s134542708.websitehome.co.uk/pillboxes/html/cubes_0.html| title=Images of anti-tank cubes.| work=Pillboxes UK| access-date=8 July 2006| archive-url=https://web.archive.org/web/20070928004236/http://s134542708.websitehome.co.uk/pillboxes/html/cubes_0.html| archive-date=28 September 2007}}</ref> In a few places, anti-tank walls were constructed{{spaced en dash}}essentially continuously abutted cubes.{{sfn|Ruddy|2003|p=29}}{{sfn|Foot|2006|p=45}}
{{multiple image|perrow=2/2|total_width=330|caption_align=center
| align = right
| image_style = border:none;
| image1 =Hairpins, Narborough.jpg
| image2 =Hedgehog sockets, Nr. Crofton on Kennet and Avon Canal.JPG
| image3 =WWII Mine sockets at Blacksmith's Bridge, Basingstoke Canal (Detail).jpg
| image4 =The Home Guard 1939-45 H15191.jpg
| footer = {{font|size=100%|font=Sans-serif|text=Top left: 'Hair pins' at [[Narborough, Norfolk]]. Top right: Sockets for a hedgehog removable roadblock on a bridge over the [[Kennet and Avon Canal]]. Bottom left: Sockets for anti-tank mines on a bridge over the [[Basingstoke Canal]]. Bottom right: Home Guard soldiers in York prepare a roadblock by inserting metal girders into pre-dug holes in the road, 2 November 1941.}}
}}
Large cylinders were made from a section of sewer pipe {{convert|3|to|4|ft|cm}} in diameter filled with concrete typically to a height of {{convert|4|to|5|ft|m}}, frequently with a dome at the top. Smaller cylinders cast from concrete are also frequently found.{{sfn|Ruddy|2003|p=28}}<ref>{{cite web| url=http://s134542708.websitehome.co.uk/pillboxes/html/cylinders_0.html| title=Images of Anti-tank cylinders| work=Pillboxes UK| access-date=8 July 2006| archive-url=https://web.archive.org/web/20070928004206/http://s134542708.websitehome.co.uk/pillboxes/html/cylinders_0.html| archive-date=28 September 2007}}</ref>
Pimples, popularly known as [[Dragon's teeth (fortification)|Dragon's teeth]], were pyramid-shaped concrete blocks designed specifically to counter tanks which, attempting to pass them, would climb up exposing vulnerable parts of the vehicle and possibly slip down with the tracks between the points. They ranged in size somewhat, but were typically {{convert|2|ft|cm}} high and about {{convert|3|ft|cm}} square at the base. There was also a conical form.{{sfn|Ruddy|2003|p=26}}<ref>{{cite web| url=http://s134542708.websitehome.co.uk/pillboxes/html/dragons_teeth_0.html| title=Images of Anti-tank pimples| work=Pillboxes UK| access-date=8 July 2006| archive-url=https://web.archive.org/web/20070501061739/http://s134542708.websitehome.co.uk/pillboxes/html/dragons_teeth_0.html| archive-date=1 May 2007}}</ref>
Cubes, cylinders and pimples were deployed in long rows, often several rows deep, to form anti-tank barriers at beaches and inland. They were also used in smaller numbers to block roads. They frequently sported loops at the top for the attachment of barbed wire. There was also a [[tetrahedral]] or [[caltrop]]-shaped obstacle, although it seems these were rare.<ref>{{cite web| url=http://archaeologydataservice.ac.uk/archives/view/dob/ai_full_r.cfm?refno=5658 | work=Defence of Britain Archive| title=Caltrop | access-date=3 January 2017}}</ref>
Where natural anti-tank barriers needed only to be augmented, concrete or wooden posts sufficed.{{unreliable source?|date=April 2021}}<ref>[[:File:Obstacles on Taunton Stop Line.JPG|Image of concrete anti-vehicle posts near Donyatt]].</ref><ref>[[:File:Anti-vehicle post, Crookham Warf.JPG|Image of wooden anti-vehicle post at Crookham Wharf]].</ref>
Roads offered the enemy fast routes to their objectives and consequently they were blocked at strategic points. Many of the road-blocks formed by Ironside were semi-permanent. In many cases, Brooke had these removed altogether, as experience had shown they could be as much of an impediment to friends as to foes. Brooke favoured removable blocks.{{sfn|Ruddy|2003|p=27}}
The simplest of the removable roadblocks consisted of concrete anti-tank cylinders of various sizes but typically about {{convert|3|ft|m}} high and {{convert|2|ft|cm}} in diameter; these could be manhandled into position as required.{{sfn|Lowry|2004|p=25}} Anti-tank cylinders were to be used on roads, and other hard surfaces; deployed irregularly in five rows with bricks or kerbstones scattered nearby to stop the cylinders moving more than {{convert|2|ft|m|abbr=on}}. Cylinders were often placed in front of socket roadblocks as an additional obstacle.{{unreliable source?|date=April 2021}}<ref>{{cite web |title=Site Type Guide: Anti Tank Blocks |url=https://ukswwh.wordpress.com/site-type-guide/anti-tank-blocks/ |website=UK Second World War Heritage |date=May 2020 |access-date=30 January 2021}}</ref> One common type of removable anti-tank roadblock comprised a pair of massive concrete buttresses permanently installed at the roadside; these buttresses had holes and/or slots to accept horizontal railway lines or [[I-beam|rolled steel joists (RSJs)]]. Similar blocks were placed across railway tracks<ref>[[:File:Railway block on Taunton Stop Line.JPG|Image of removable railblock buttresses on the Taunton Stop Line near Donyatt]].</ref> because tanks can move along railway lines almost as easily as they can along roads.<ref name = RobOsborn>{{cite web| url=http://www.yeovilhistory.info/roadblock.htm| title=Road and Rail blocks | author = Bob Osborn | year = 2019 | work=Yeovil's Virtual Museum | access-date=9 January 2022}} A rare extant example.</ref> These blocks would be placed strategically where it was difficult for a vehicle to go around{{spaced en dash}}anti-tank obstacles and mines being positioned as required{{spaced en dash}}and they could be opened or closed within a matter of minutes.<ref name = RobOsborn/><ref>{{cite web| title=Imperial War Museum Collection Search | work=Photograph number H 7330, Home Guards erecting a road barrier | url=http://www.iwm.org.uk/collections/item/object/205195194 | access-date=29 June 2012}}</ref>
[[File:Railway block on Taunton Stop Line.JPG|thumb|left|Removable roadblock buttress on the [[Taunton Stop Line]]]]
There were two types of socket roadblocks. The first comprised vertical lengths of railway line placed in sockets in the road and was known as hedgehogs.<ref>{{cite web| url=http://s134542708.websitehome.co.uk/pillboxes/html/hedgehog.html| title=Images of Hedgehog obstacles| work=Pillboxes UK| access-date=24 May 2006| archive-url=https://web.archive.org/web/20070427171917/http://s134542708.websitehome.co.uk/pillboxes/html/hedgehog.html| archive-date=27 April 2007}}</ref><ref>{{cite web | title=Imperial War Museum Collection Search | work=Photograph number H 15191, Home Guard soldiers prepare a roadblock by inserting metal girders into pre-dug holes in the road (image) | url=http://www.iwm.org.uk/collections/item/object/205198203 | access-date=29 June 2012}}</ref> The second type comprised railway lines or RSJs bent or welded at around a 60° angle, known as hairpins.{{sfn|Lowry|2004|p=20}}<ref>{{cite web| url=http://s134542708.websitehome.co.uk/pillboxes/html/hairpin.html| title=Images of Hairpin obstacles| work=Pillboxes UK| access-date=22 June 2006| archive-url=https://web.archive.org/web/20070501134739/http://s134542708.websitehome.co.uk/pillboxes/html/hairpin.html| archive-date=1 May 2007}}</ref> In both cases, prepared sockets about {{convert|6|in|mm|2}} square were placed in the road, closed by covers when not in use, allowing traffic to pass normally.<ref>{{cite web| url=http://archaeologydataservice.ac.uk/catalogue/adsdata/oasis_reports/contexto1/ahds/dissemination/pdf/contexto1-73825_1.pdf| title=Land off Morton Way, Axminster, Devon&nbsp;– A Limited Archaeological Excavation and Recording Programme | publisher = Context One Archaeological Services 2010 | year = 2010 | work=Archaeology Data Service | access-date=14 May 2011}}</ref>
Another removable roadblocking system used mines. The extant remains of such systems superficially resemble those of hedgehog or hairpin, but the pits are shallow: just deep enough to take an anti-tank mine. When not in use the sockets were filled with wooden plugs, allowing traffic to pass normally.<ref>{{cite web|url=http://www.pillbox-study-group.org.uk/basingstokeantitankexcavation.htm |title=Basingstoke Canal Anti-Tank Cylinder & Mine Socket Excavation |author=Tim Denton |work=Pillboxes UK |access-date=5 March 2009 |archive-url=https://web.archive.org/web/20100101224456/http://www.pillbox-study-group.org.uk/basingstokeantitankexcavation.htm |archive-date=1 January 2010 }}</ref>
Bridges and other key points were prepared for demolition at short notice by preparing chambers filled with explosives. A Depth Charge Crater was a site in a road (usually at a junction) prepared with buried explosives that could be detonated to instantly form a deep crater as an anti-tank obstacle. The [[Canadian pipe mine]] (later known as the McNaughton Tube after [[Andrew McNaughton|General Andrew McNaughton]]) was a [[Directional drilling|horizontally bored]] pipe packed with explosives{{spaced en dash}}once in place this could be used to instantly ruin a road or runway.{{sfn|Cameron|2006|p=156}}<ref>{{cite news
| url=http://news.bbc.co.uk/1/hi/england/hampshire/4934102.stm
| title=Large bomb found at ex-Navy base
|work=BBC News
| access-date=12 January 2012
| date=22 April 2006 }}
</ref><ref>{{cite magazine
| url=https://www.wired.com/dangerroom/2007/08/frontline-bri-1/
| title=Robodigger Vs Canadian Threat
| magazine=Wired
| access-date=12 January 2012
| date=30 August 2007
| first=David
| last=Hambling}}
</ref> Prepared demolitions had the advantage of being undetectable from the air{{spaced en dash}}the enemy could not take any precautions against them, or plot a route of attack around them.
[[File:Demolition chambers, Mausel Lock.JPG|thumb|Demolition chambers under a bridge over the [[Bridgwater and Taunton Canal]]{{spaced en dash}}later filled with concrete]]
Crossing points in the defence network{{spaced en dash}}bridges, tunnels and other weak spots{{spaced en dash}}were called nodes or points of resistance. These were fortified with removable road blocks, barbed wire entanglements and land mines. These passive defences were overlooked by trench works, gun and mortar emplacements, and pillboxes. In places, entire villages were fortified using barriers of Admiralty scaffolding, [[sandbag]]ged positions and [[British hardened field defences of World War II#Loopholed Walls and Defended Buildings|loopholes]] in existing buildings.{{sfn|Foot|2006|p=11}}
Nodes were designated 'A', 'B' or 'C' depending upon how long they were expected to hold out.{{sfn|Foot|2006|p=10}} Home Guard troops were largely responsible for the defence of nodal points and other centres of resistance, such as towns and defended villages. Category 'A' nodal points and anti-tank islands were usually garrisoned by regular troops.{{sfn|Foot|2006|p=4}}
The rate of construction was frenetic: by the end of September 1940, 18,000 pillboxes and numerous other preparations had been completed.{{sfn|Cruickshank|2001|p=166}}  Some existing defences such as mediaeval castles and Napoleonic forts were augmented with modern additions such as dragon's teeth and pillboxes; some Iron Age forts housed anti-aircraft and observer positions.{{Sfn|Warner|1980|p=89}}  About 28,000 pillboxes and other hardened field fortifications were constructed in the United Kingdom of which about 6,500 still survive.<ref name = dob_review >{{cite web | title=A Review of the Defence of Britain Project | work=Report | url=http://www.britarch.ac.uk/projects/dob/review/index.html | access-date=30 May 2006 | archive-date=23 November 2007 | archive-url=https://web.archive.org/web/20071123103253/http://www.britarch.ac.uk/projects/dob/review/index.html }}</ref>  Some defences were disguised and examples are known of pillboxes constructed to resemble haystacks, logpiles and innocuous buildings such as churches and railway stations.{{Sfn|Warner|1980|p=89}}
===Airfields and open areas===
[[File:Fully enclosed Bison 2342A1.jpg|thumb|right|[[Bison concrete armoured lorry]]]]
Open areas were considered vulnerable to invasion from the air: a landing by paratroops, glider-borne troops or powered aircraft which could land and take off again. Open areas with a straight length of {{convert|500|yd}} or more within five&nbsp;miles (8&nbsp;km) of the coast or an airfield were considered vulnerable. These were blocked by trenches or, more usually, by wooden or concrete obstacles, as well as old cars.<ref>{{cite web| title=Imperial War Museum Collection Search | work=Photograph number D 4282. Obstacles in a field (image) | url=http://www.iwm.org.uk/collections/item/object/205198730 | access-date=29 June 2012}}</ref><ref>{{cite web
| url        = http://www.historic-cornwall.org.uk/flyingpast/fear.html#beach
| title      = Fear of Invasion&nbsp;– Beach Defences
| work       = Historic Cornwall
| access-date =4 August 2010
}}</ref>
Securing an airstrip would be an important objective for the invader.{{sfn|Ward|1997|p=65}} Airfields, considered extremely vulnerable, were protected by trench works and pillboxes that faced inwards towards the runway, rather than outwards. Many of these fortifications were specified by the [[Air Ministry]] and defensive designs were unique to airfields{{spaced en dash}}these would not be expected to face heavy weapons so the degree of protection was less and there was more emphasis on all-round visibility and sweeping fields of fire. It was difficult to defend large open areas without creating impediments to the movement of friendly aircraft. Solutions to this problem included the pop-up [[Pickett-Hamilton Fort|Picket Hamilton fort]]{{spaced en dash}}a light pillbox that could be lowered to ground level when the airfield was in use.<ref>{{cite web| url=http://www.users.globalnet.co.uk/~rwbarnes/defence/silloth_/phfort-.htm| title=Pickett-Hamilton Fort | access-date=11 June 2006}}</ref><ref>{{cite web | url=http://s134542708.websitehome.co.uk/pillboxes/html/pickett_hamilton_pillbox.html | title=Picket-Hamilton fort | work=Pillboxes UK | access-date=14 March 2007 | archive-url=https://web.archive.org/web/20070928004351/http://s134542708.websitehome.co.uk/pillboxes/html/pickett_hamilton_pillbox.html | archive-date=28 September 2007}}</ref>
{{Multiple image|total_width=300
|image1=Eglinton tree grubber.JPG
|alt1=
|caption1=The Canadian runway 'plough'
|image2=Image-Pillbox at Curzon Bridges (North).JPG
|alt2=
|caption2=Pillbox type FW3/22
}}
Another innovation was a mobile pillbox that could be driven out onto the airfield. This was known as the [[Bison concrete armoured lorry|Bison]] and consisted of a lorry with a concrete armoured cabin and a small concrete pillbox on the flat bed.<ref>{{cite web | url=http://s134542708.websitehome.co.uk/pillboxes/html/bison_pillbox.html | title=Bison mobile pillbox | work=Pillboxes UK | access-date=14 March 2007 | archive-url=https://web.archive.org/web/20070928004221/http://s134542708.websitehome.co.uk/pillboxes/html/bison_pillbox.html | archive-date=28 September 2007}}</ref><ref>{{cite web| url=http://www.warwheels.net/ThorneycroftBisonBovingtonTROWBRIDGE.html | title=Thorneycroft Bison | work=War Wheels.net | access-date=14 March 2007}}</ref>
Constructed in Canada, a 'runway plough', assembled in Scotland, survives at [[Eglinton Country Park]]. It was purchased by the army in World War II to rip up aerodrome runways and railway lines, making them useless to the occupying forces, if an invasion took place. It was used at the old Eglinton Estate, which had been commandeered by the army, to provide its army operators with the necessary experience. It was hauled by a powerful [[Foden Trucks]] tractor, possibly via a pulley and cable system.<ref name="Archive">Eglinton Country Park archive.</ref>
==Other defensive measures==
Other basic defensive measures included the removal of signposts, milestones (some had the carved details obscured with cement) and [[Running in board|railway station signs]], making it more likely that an enemy would become confused.<ref>{{cite web | title=Imperial War Museum Collection Search | work=Photograph number HU 49250, A signpost in Surrey being dismantled (image) | url=http://www.iwm.org.uk/collections/item/object/205019014 | access-date=29 June 2012}}</ref> Petrol pumps were removed from [[Filling station|service stations]] near the coast and there were careful preparations for the destruction of those that were left.<ref name = Evans_p64>{{harvnb|Evans|2004|p=64}}</ref> Detailed plans were made for destroying anything that might prove useful to the invader such as port facilities, key roads and [[rolling stock]].{{sfn|Churchill|1949|p=156}} In certain areas, [[Evacuations of civilians in Britain during World War II|non-essential citizens were evacuated]]. In the county of [[Kent]], 40% of the population was relocated; in [[East Anglia]], the figure was 50%.<ref name=Evans_p64/>
Perhaps most importantly, the population was told what was expected from them. In June 1940, the [[Ministry of Information (United Kingdom)|Ministry of Information]] published ''If the Invader Comes, what to do{{spaced en dash}}and how to do it''.<ref>{{harvnb|Lowry|2004|p= 43}}</ref><ref>{{cite web| url=http://www.swanseaheritage.net/article/gat.asp?ARTICLE_ID=1865&PRIMARY_THEME_ID=3| title=If the Invader Comes, leaflet| access-date=15 May 2006| archive-url=https://web.archive.org/web/20070927161433/http://www.swanseaheritage.net/article/gat.asp?ARTICLE_ID=1865&PRIMARY_THEME_ID=3| archive-date=27 September 2007}}</ref> It began:
{{cquote|The Germans threaten to invade Great Britain. If they do so they will be driven out by our Navy, our Army and our Air Force. Yet the ordinary men and women of the civilian population will also have their part to play. [[Adolf Hitler|Hitler's]] invasions of Poland, Holland and Belgium were greatly helped by the fact that the civilian population was taken by surprise. They did not know what to do when the moment came. ''You must not be taken by surprise.'' This leaflet tells you what general line you should take. More detailed instructions will be given you when the danger comes nearer. Meanwhile, read these instructions carefully and be prepared to carry them out. [Emphasis as in original].<ref name="invader">{{cite web| url=http://www.historylearningsite.co.uk/home_front.htm| work=History Learning Site| title=If the Invader Comes, what to do&nbsp;– and how to do it. Full text | access-date=16 April 2007}}</ref>}}
The first instruction given quite emphatically is that, unless ordered to evacuate, "the order ...[was]... to 'stay put'". The roads were not to be blocked by refugees. Further warnings were given not to believe rumours and not to spread them, to be distrustful of orders that might be faked and even to check that an officer giving orders really was British. Further: Britons were advised to keep calm and report anything suspicious quickly and accurately; deny useful things to the enemy such as food, fuel, maps or transport; be ready to block roads{{spaced en dash}}when ordered to do so{{spaced en dash}}"by felling trees, wiring them together or blocking the roads with cars"; to organise resistance at shops and factories; and, finally: "Think before you act. But think always of your country before you think of yourself".<ref name="invader"/>
On 13 June 1940, the ringing of church bells was banned; henceforth, they would only be rung by the military or the police to warn that an invasion{{spaced en dash}}generally meaning by parachutists{{spaced en dash}}was in progress.{{sfn|Fleming|1957|p=96}}
More than passive resistance was expected{{spaced en dash}}or at least hoped for{{spaced en dash}}from the population. Churchill considered the formation of a Home Guard Reserve, given only an armband and basic training on the use of simple weapons, such as Molotov cocktails. The reserve would only have been expected to report for duty in an invasion.{{sfn|Churchill|1949|p=582}} Later, Churchill wrote how he envisaged the use of the sticky bomb, "We had the picture in mind that devoted soldiers ''or civilians'' would run close up to the tank and even thrust the bomb upon it, though its explosion cost them their lives [Italics added for emphasis]."{{sfn|Churchill|1949|p=149}} The prime minister practised shooting, and told wife [[Clementine Churchill|Clementine]] and daughter in law [[Pamela Churchill|Pamela]] that he expected them each to kill one or two Germans. When Pamela protested that she did not know how to use a gun, Churchill told her to use a kitchen butcher knife as "You can always take a Hun with you".<ref name="lastlion2012">{{harvnb|Manchester|Reid|2012|loc=location 4263–4273}}</ref> He later recorded how he intended to use the slogan "[[British propaganda during World War II|You can always take one with you.]]"{{sfn|Churchill|1949|p=246}}
In 1941, in towns and villages, invasion committees were formed to cooperate with the military and plan for the worst should their communities be isolated or occupied.<ref>{{cite web | title=Imperial War Museum Collection Search| work=Photograph number D 4847, Village Invasion Committee meeting (image) | url=http://www.iwm.org.uk/collections/item/object/205198790 | access-date=29 June 2012}}</ref> The members of committees typically included representatives of the local council, the [[Air Raid Precautions]] service, the fire service, the police, the [[WRVS|Women's Voluntary Service]] and the Home Guard, as well as officers for medicine, sanitation and food. The plans of these committees were kept in secret ''War Books'', although few remain. Detailed inventories of anything useful were kept: vehicles, animals and basic tools, and lists were made of contact details for key personnel. Plans were made for a wide range of emergencies, including improvised mortuaries and places to bury the dead.<ref>{{cite web | url=http://www.britannia.com/lympstone/warbook.html | title=The History of WWII Invasion Committee "War Books" | author=Ian F Angus | access-date=29 July 2006 | archive-url=https://web.archive.org/web/20060827022954/http://www.britannia.com/lympstone/warbook.html | archive-date=27 August 2006 }}</ref> Instructions to the invasion committees stated: "...&nbsp;every citizen will regard it as his duty to hinder and frustrate the enemy and help our own forces by every means that ingenuity can devise and common sense suggest."<ref>Consolidated Instructions to Invasion Committees, 1942, p. 19.</ref>
At the outbreak of the war there were around 60,000 police officers in the United Kingdom, including some 20,000 in London's [[Metropolitan Police]].<ref name=police/>  Many younger officers joined the armed forces and numbers were maintained by recruiting "war reserve" officers, [[special constable]]s and by recalling retired officers.<ref name=police/>{{Sfn|Gould|Waldren|1986|p=103}}  As well as their usual duties the police, who are a generally unarmed force in Britain, took on roles checking for enemy agents and arresting deserters.<ref name=police>{{cite web |title=Police during the Second World War |url=http://www.open.ac.uk/Arts/history-from-police-archives/PolCit/polww2.html |website=International Centre for the History of Crime, Policing and Justice |publisher=Open University |access-date=2 April 2021}}</ref>
On the same day as the [[Battle of Dunkirk]], [[Scotland Yard]] issued a memorandum detailing the [[Police use of firearms in the United Kingdom|police use of firearms]] in wartime. This detailed the planned training for all officers in the use of pistols and revolvers, as it was decided that even though the police were non-combatant, they would provide armed guards at sites deemed a risk from enemy sabotage, and defend their own police stations from enemy attack.{{Sfn|Gould|Waldren|1986|p=103}}  A supplementary secret memorandum of 29 May also required the police to carry out armed motorised patrols of 2–4 men, if invasion happened, though it noted the police were a non-combatant force and should primarily be carrying out law enforcement duties.{{Sfn|Gould|Waldren|1986|p=104}}  These arrangements led to high level political discussions; on 1 August 1940 [[Lord Mottisone]], a former cabinet minister, telephoned Churchill to advise that current police regulations would require officers to prevent British civilians resisting the German forces in occupied areas.{{Sfn|Churchill|Gilbert|1983|p=711}}  Churchill considered this unacceptable and he wrote to the home secretary, [[John Anderson, 1st Viscount Waverley|John Anderson]], and Lord Privy Seal, [[Clement Attlee]], asking for the regulations to be amended. Churchill wanted the police, ARP wardens and firemen to remain until the last troops withdrew from an area and suggested that such organisations might automatically become part of the military in case of invasion.{{Sfn|Churchill|1949|p=418}}{{Sfn|Rowe|2011|p=99}}  The War Cabinet discussed the matter and on 12 August Churchill wrote again to the home secretary stating that the police and ARP wardens should be divided into two arms, combatant and non-combatant. The combatant portion would be armed and expected to fight alongside the Home Guard and regular forces and would withdraw with them as necessary. The non-combatant portion would remain in place under enemy occupation, but under orders not to assist the enemy in any way even to maintain order.{{Sfn|Churchill|1949|p=422}}  These instructions were issued to the police by a memorandum from Anderson on 7 September, which stipulated that the non-combatant portion should be a minority and, where possible, made up of older men and those with families.{{Sfn|Rowe|2011|p=99}}
Because of the additional armed duties the number of firearms allocated to the police was increased. On 1 June 1940 the Metropolitan Police received 3,500 Canadian [[Ross Rifle]]s of First World War vintage. A further 50 were issued to the [[London Fire Brigade]] and 100 to the [[Port of Tilbury Police|Port of London Authority Police]].{{Sfn|Gould|Waldren|1986|p=105}}  Some 73,000 rounds of [[.303 British|.303 rifle ammunition]] were issued, together with tens of thousands of .22 rounds for small bore rifle and pistol training.{{Sfn|Gould|Waldren|1986|p=105}}  By 1941 an additional 2,000 automatic pistols and 21,000 American lend-lease revolvers had been issued to the Metropolitan Police; from March 1942 all officers above the rank of inspector were routinely armed with .45 revolvers and twelve rounds of ammunition.{{Sfn|Gould|Waldren|1986|p=107}}
==Guns, petroleum and poison==
{{See also|Petroleum Warfare Department}}
[[File:D 024854 new.jpg|thumb|right|A [[flame fougasse]] demonstration somewhere in Britain. A car is surrounded in flames and a huge cloud of smoke. circa 1940.]]
In 1940, weapons were critically short; there was a particular scarcity of anti-tank weapons, many of which had been left in France. Ironside had only 170 2-pounder anti-tank guns but these were supplemented by 100 Hotchkiss 6-pounder guns dating from the First World War,<ref>{{harvnb|Foot|2006|p=7}}</ref> improvised into the anti-tank role by the provision of solid shot.{{sfn|Lowry|2004|p=20}} By the end of July 1940, an additional nine hundred 75&nbsp;mm field guns had been received from the US{{sfn|Churchill|1949|p=238}}{{spaced en dash}}the British were desperate for any means of stopping armoured vehicles. The [[Sten]] submachine gun was developed following the fall of France, to supplement the limited number of [[Thompson submachine gun]]s obtained from the United States.{{sfn|Parker|1967|p=26}}
One of the few resources not in short supply was petroleum oil; supplies intended for Europe were filling British storage facilities.{{sfn|Banks|1946|p=27}} Considerable effort and enthusiasm was put into making use of petroleum products as a weapon of war. The Army had not had flame-throwers since the First World War, but a significant number were improvised from pressure greasing equipment acquired from automotive repair garages. Although limited in range, they were reasonably effective.{{sfn|White|1955|p=16}}
A mobile flame trap comprised surplus bulk storage tanks on trucks, the contents of which could be hosed into a [[Sunken lane|sunken road]] and ignited. A static flame trap was prepared with perforated pipes running down the side of a road connected to a {{convert|600|impgal|L USgal|-1|adj=on}} elevated tank; some 200 of these traps were installed.{{sfn|Warner|1980|p=163}}{{sfn|Hayward|2001|pp=15–17}} Usually, gravity sufficed but in a few cases a pump assisted in spraying the mixture of oil and petrol.{{sfn|Hayward|2001|pp=15–17}}
A [[flame fougasse]] comprised a 40-gallon light steel drum{{refn|Although the standard capacity is 44 imperial gallons (55 US gallons), historical records generally refer to 40-gallon drums and sometimes 50-gallon drums apparently interchangeably.|group="nb"}} filled with petroleum mixture and a small, electrically detonated explosive. This was dug into the roadside with a substantial overburden and camouflaged. [[Ammonal]] provided the propellant charge, it was placed behind the barrel and, when triggered, caused the barrel to rupture and shoot a jet of flame {{convert|10|ft|m}} wide and {{convert|30|yd|m}} long.<ref>Barrel Flame Traps, 1942.</ref><ref name = "Fred Lord Hilton" >{{cite web
| title      = Recollections of Fred Lord Hilton MM&nbsp;– witness to a flame fougasse demonstration
| work      = WW2 People's War (BBC)
| url      = http://www.bbc.co.uk/ww2peopleswar/stories/71/a8090471.shtml
| access-date      = 3 November 2011
| archive-date      = 22 July 2012
| archive-url      = https://archive.today/20120722124219/http://www.bbc.co.uk/ww2peopleswar/stories/71/a8090471.shtml
}}</ref> They were usually deployed in batteries of four barrels{{sfn|Evans|2004|p=62}} and would be placed at a location such as a corner, steep incline or roadblock where vehicles would be obliged to slow.<ref>{{cite web|title=Flame Fougasse (surviving remains) |work=Pillbox Study Group |author=Adrian Armishaw |url=http://www.pillbox-study-group.org.uk/poyningsflametrappage.htm |access-date=15 January 2008 |archive-url=https://web.archive.org/web/20080118202057/http://www.pillbox-study-group.org.uk/poyningsflametrappage.htm |archive-date=18 January 2008 }}</ref>
Variants of the flame fougasse included the demigasse, a barrel on its side and left in the open with explosive buried underneath; and the hedge hopper: a barrel on end with explosive buried underneath a few inches deep and slightly off centre. On firing, the hedge hopper barrel was projected {{convert|10|ft|m|spell=in}} into the air and over a hedge or wall behind which it had been hidden.{{sfn|Hayward|2001|p=19}}<ref>{{cite web | title=Memoirs of William Leslie Frost, a member of the Home Guard who recalled the hedge hopper weapon in action | work=South Staffordshire Home Guard website | url=http://www.staffshomeguard.co.uk/DotherReminiscences3staffshg.htm | access-date=16 July 2006}}</ref> 50,000 flame fougasse barrels were installed at 7,000 sites mostly in southern England and at a further 2,000 sites in Scotland.{{sfn|Banks|1946|p=38}}
[[File:A BCV (Bulk Contamination Vehicle.jpg|thumb|right|upright|Chemical warfare bulk contamination vehicle circa 1940]]
Early experiments with floating petroleum on the sea and igniting it were not entirely successful: the fuel was difficult to ignite, large quantities were required to cover even modest areas and the weapon was easily disrupted by waves. However, the potential was clear. By early 1941, a flame barrage technique was developed. Rather than attempting to ignite oil floating on water, nozzles were placed above high-water mark with pumps producing sufficient pressure to spray fuel, which produced a roaring wall of flame over, rather than on, the water.{{sfn|Cameron|2006|pp=163–164}} Such installations consumed considerable resources and although this weapon was impressive, its network of pipes was vulnerable to pre-landing bombardment; General Brooke did not consider it effective.{{sfn|Alanbrooke|2001|loc=Entry 24 February 1941}} Initially ambitious plans were cut back to cover just a few miles of beaches.{{sfn|Hayward|2001|pp=19–25}}<ref>{{cite web | title=Imperial War Museum Collection Search | work=Images of petroleum warfare | url=http://www.iwm.org.uk/collections/search?query=fougasse&submit=&items_per_page=10&filter%5bwebCategory%5d%5b0%5d=%22photographs%22 | access-date=29 June 2012}}</ref>  The tests of some of these installations were observed by German aircraft; the British capitalised on this by dropping propaganda leaflets into occupied Europe referring to the effects of the petroleum weapons.{{Sfn|Warner|1980|p=164}}
It seems likely the British would have used poison gas against troops on beaches. General Brooke, in an annotation to his published war diaries, stated that he "''...&nbsp;had every intention of using sprayed [[mustard gas]] on the beaches''".{{sfn|Alanbrooke|2001|loc=Entry 22 July 1940}} Mustard gas was manufactured as well as [[chlorine]], [[phosgene]] and [[Paris Green]]. Poison gases were stored at key points for use by Bomber Command and in smaller quantities at many more airfields for use against the beaches. Bombers and crop sprayers would spray landing craft and beaches with mustard gas and Paris Green.<ref>{{cite web | url=http://www.bpears.org.uk/Misc/War_NE/w_section_05.html | title=Rowlands Gill and the North-East, 1939–1945 | work=Chapter 5: Invasion | author=Brian Pears | access-date=28 July 2006 | archive-url=https://web.archive.org/web/20060806075839/http://www.bpears.org.uk/Misc/War_NE/w_section_05.html | archive-date=6 August 2006}}</ref>{{sfn|Ward|1997|p=83}}<ref>{{cite web | url=http://www.rafmuseum.org/london/collections/aircraft/de-havilland-tiger-moth-ii.cfm | title=de Havilland Tiger Moth II | work=RAF Museum, London | access-date=18 June 2008 | archive-url=https://web.archive.org/web/20081013010709/http://www.rafmuseum.org/london/collections/aircraft/de-havilland-tiger-moth-ii.cfm | archive-date=13 October 2008}}</ref>
==Deception and disinformation==
{{Main|London Controlling Section|Political Warfare Executive}}
{{See also|Petroleum Warfare Department#Burning seas}}
In addition to hiding real weapons and fortifications, steps were taken to create the impression of the existence of defences that were not real. Drain pipes stood in place of real guns,<ref>{{cite web
|title        = Drain Pipes For Defences
|author       = Mike Stapleton
|work         = WW2 People's War (BBC)
|url          = http://www.bbc.co.uk/ww2peopleswar/stories/33/a4038833.shtml
|access-date  = 3 November 2011
|archive-date = 22 July 2012
|archive-url  = https://archive.today/20120722103214/http://www.bbc.co.uk/ww2peopleswar/stories/33/a4038833.shtml
}}</ref> dummy pillboxes were constructed,{{sfn|Wills|1985|p=63}}<ref>{{cite web | title=Imperial War Museum Collection Search | work=Photograph number F 4022, Dummy pillbox constructed in France | url=http://www.iwm.org.uk/collections/item/object/205204917 | access-date=29 June 2012}}</ref> and uniformed [[mannequins]] kept an unblinking [[wikt:vigil|vigil]].{{sfn|Cox|1974|loc=plate p. 94}}
Volunteers were encouraged to use anything that would delay the enemy. A young member of the Home Guard (LDV) recalled:
{{blockquote|In the villages use was made of any existing walls or buildings, loopholes for firing or passing heavy chains and cables through to form barriers strong enough to slow down or stop soft skinned vehicles. The chains and cables could also be made into psychological barriers to tanks by attaching an imitation bomb to them, an impression which could be augmented by running a length of cable from it to a position out of sight of a tank commander. These positions could be made even more authentic by breaking up the surface immediately in front of the obstacle and burying an old soup plate, or similar object. For occasions where time did not permit the passing of cables and chains we had concrete cylinders the size of a 45&nbsp;gallon oil or tar barrel ready to roll into a roadway or other gap. These generally had a large metal loop cemented into one end through which a cable could be passed to link several together. Again, suspicious looking parcels could be attached to strengthen the illusion.<ref>{{cite web | title=Leonard Thomas Piper | work=WW2 People's War (article a2504530) | url=https://www.bbc.co.uk/ww2peopleswar/stories/30/a2504530.shtml | access-date=20 July 2006}}</ref>}}
In 1938, a section funded by [[MI6]] was created for propaganda, headed by Sir [[Campbell Stuart]]. It was allocated premises at [[Electra House]] and was dubbed Department EH. On 25 September 1939, the unit was mobilised to [[Woburn Abbey]]<ref>{{cite web | title=The Major Developments In Political Warfare Through The War, 1938–1945 (typeset from National Archive CAB 101/131) | year = 1949 | author = Y. M. Streatfield | work=PsyWar.org | url=http://www.psywar.org/psywar/reproductions/pwe_report.pdf | access-date=14 July 2007}}</ref> where it joined a subversion team from MI6, known as Section D, and by July these teams became a part of the newly created [[Special Operations Executive]] (SOE).{{sfn|Hayward|2001|pp=40–45}} These SOE elements went on to form the core of the [[Political Warfare Executive]] in 1941. Their task was to spread false rumours and conduct [[psychological warfare]]. Inspired by a demonstration of petroleum warfare, one false rumour stated that the British had a new bomb: dropped from an aircraft, it caused a thin film of volatile liquid to spread over the surface of the water which it then ignited.{{sfn|White|1955|loc=chapter 1}} Such rumours were credible and rapidly spread. American broadcaster [[William Shirer]] recorded large numbers of burns victims in Berlin; though it is not clear what he personally saw, it seems likely his reports were influenced by rumours. The interrogation of a Luftwaffe pilot revealed the existence of such weapons was common knowledge,<ref>{{cite web | title=Whispers of War&nbsp;– The British World War II rumour campaign | work=Lee Richards | url=http://www.psywar.org/sibs.php | access-date=31 May 2006 | archive-date=28 November 2020 | archive-url=https://web.archive.org/web/20201128161146/https://www.psywar.org/sibs.php }}</ref> and documents found after the war showed the German high command were deceived.<ref>{{cite web | title=Deception and Disinformation | work=Herb Friedman | url=http://www.psywarrior.com/DeceptionH.html | access-date=31 May 2006}}</ref> The rumour seemed to take on a life of its own on both sides leading to persistent stories of a thwarted German invasion, in spite of official British denials.{{sfn|Churchill|1949|p=275}}{{sfn|Hayward|2001}}{{sfn|Gillies|2006|pp=293–294}} On 15 December 1940, ''The New York Times'' ran a story claiming that tens of thousands of German troops had been 'consumed by fire' in two failed invasion attempts.<ref>{{cite news | title=Nazi Invaders Held 'Consumed by Fire' | work=The New York Times | date=15 December 1940 | url=https://pqasb.pqarchiver.com/nytimes/95789986.html?did=95789986&FMT=ABS&FMTS=AI&date=Dec+15%2C+1940&author=By+BORIS+NIKOLAYEVSKY+North+American+Newspaper+Alliance&pub=New+York+Times++(1857-Current&desc=NAZI+INVADERS+HELD+%27CONSUMED+BY+FIRE%27 | access-date=31 May 2006 }}{{dead link|date=July 2024|bot=medic}}{{cbignore|bot=medic}}</ref>
==Planned resistance==
{{Main|Auxiliary Units}}
The War Office did not treat the threat of invasion seriously until the collapse of France in May 1940. The [[Secret Intelligence Service]] had, however, been making plans for this eventuality since February 1940, creating the core of a secret resistance network across the country. This remained in existence until at least 1943 and comprised both intelligence and sabotage units. In May 1940, SIS also began to distribute arms dumps and recruit for a larger civilian guerrilla organisation called the Home Defence Scheme. This was deeply resented by the War Office who created the Auxiliary Units as a more respectable military alternative.{{sfn|Atkin|2015|loc = Chapters 4 and 11}}
Auxiliary Units were a specially trained and secret organisation that would act as uniformed commandos to attack the flanks and rear of an enemy advance. They were organised around a core of regular army 'scout sections', supported by patrols of 6–8 men recruited from the Home Guard. Although approval for the organisation had been given in June 1940, recruiting only began in early July. Each patrol was a self-contained cell, expected to be self-sufficient. There was, however, no means of communicating with them once they had gone to ground, which greatly reduced their strategic value. Each patrol was well-equipped and was provided with a concealed underground operational base, usually built in woodland and camouflaged.<ref>{{cite web | title=Parham Airfield Museum | work=The Museum of the British Resistance Organisation | url=http://www.parhamairfieldmuseum.co.uk/BRO.html | access-date=11 June 2006 | archive-url=https://web.archive.org/web/20130625152725/http://www.parhamairfieldmuseum.co.uk/BRO.html | archive-date=25 June 2013}}</ref><ref>{{cite web | title=The British Resistance Movement, 1940–44 | work=Geoffrey Bradford | url=http://www.auxunit.org.uk/gbradfordintro.htm | access-date=11 June 2006}}</ref> Auxiliary Units were only expected to operate during an organised military campaign, with an expected lifespan of 14 days. They were not, therefore, intended to operate as a long term resistance organisation. The latter was the responsibility of the Secret Intelligence Service Section VII, which would have only begun to expand its operations once the country had actually been occupied, thus confining knowledge of its existence only to those men and women who would have been available at the time.{{sfn|Atkin|2015|loc = Chapters 6–8 and 11}}
In addition, the Auxiliary Units included a network of civilian Special Duties personnel, recruited to provide a short-term intelligence gathering service, spying on enemy formations and troop movements. Reports were to be collected from [[Dead drop|dead letter drops]] and, from 1941, relayed by civilian radio operators from secret locations. The wireless network only become operational from 1941 and was unlikely to survive more than a few days following invasion. Intelligence gathering after this period would be by the mobile patrols of the [[GHQ Liaison Regiment|GHQ Liaison Unit]] ('Phantom'), which were staffed by skilled linguists and equipped with powerful wireless sets for direct communication with GHQ.{{sfn|Atkin|2015|loc = Chapters 9 and 10}}
==Offensive anti-invasion operations==
[[File:40 Squadron RAF Blenheim Jul 1940 IWM CH 787.jpg|thumb|right|This [[Bristol Blenheim|Blenheim Mark VI]] bomber of [[No. 40 Squadron RAF]] was lost with its crew during a raid on German invasion barges at [[Ostend]] on 8 September 1940.]]
[[File:A 4.7-inch gun onboard HMS JUPITER firing on enemy shipping in the port of Cherbourg, on the night of 10-11 October 1940. A1010.jpg|thumb|right|{{HMS|Jupiter|F85|6}} fires her [[QF 4.7-inch Mk IX & XII naval gun|4.7-inch guns]] during [[Operation Medium]], the bombardment of [[Cherbourg]] on 10 October 1940.]]
The [[Churchill war ministry#Ministers who held war cabinet membership, 10 May 1940 – 23 May 1945|War Cabinet]] and the [[Chiefs of Staff Committee]] were not content to sit and wait for the Germans to make the first move; considerable efforts were made to attack, by air and sea, the enemy shipping which had been assembled in occupied ports between [[The Hague]] and [[Cherbourg]], starting in July 1940.<ref>The British Bombing Survey Unit (1998) [''The Strategic Air War Against Germany, 1939–1945''] Frank Cass Publishers, {{ISBN|0-7146-4722-5}} (p. 29)</ref> These attacks became known as the "Battle of the Barges".<ref>Holland, James (2010), [https://books.google.com/books?id=kPSm_J-hXPoC&dq=%22bomber+command%22+%22Battle+of+the+barges%22&pg=PA775 ''The Battle of Britain''], Corgi Books, {{ISBN|978-0-552-15610-3}} (p. 775)</ref> Some notable operations are shown below:
* 12 August: Five [[Handley Page Hampden]]s attacked the [[Ladbergen]] Aqueduct on the [[Dortmund-Ems Canal]]. The waterway was blocked for ten days, impeding the movement of barges towards the Channel ports.<ref>Donnelly, Larry (2004), [https://books.google.com/books?id=y7Xi9MWcE48C&dq=bomber+command+ladbergen&pg=PA65 ''The Other Few: The Contribution Made by Bomber and Coastal Aircrew to the Winning of the Battle of Britain''] Red Kite, {{ISBN|0-9546201-2-7}}</ref>
* 8 September: Two cruisers and ten destroyers swept along the French coast and bombarded [[Boulogne]] harbour.<ref name="naval-history.net"/> In a separate operation, three [[Motor Torpedo Boats]] attacked a convoy of small vessels off [[Ostend]]; two of the MTBs then entered the harbour and torpedoed two transport ships.<ref name="Jackson">Jackson, Robert (2013), [https://books.google.com/books?id=jYtHrfu38XYC&dq=hms+revenge+bombards+cherbourg&pg=PT81 ''Churchill's Channel War: 1939–45''] {{webarchive|url=https://web.archive.org/web/20160518231011/https://books.google.com/books?id=jYtHrfu38XYC&pg=PT81&lpg=PT81&dq=hms+revenge+bombards+cherbourg&source=bl&ots=q4kewc1Vl4&sig=scWmFiHIrttDzWWPBO9XXOxn-F8&hl=en&sa=X&ei=dvXjUorHO5GDhQf1zYCADA&ved=0CEAQ6AEwAw |date=18 May 2016 }}, Osprey Publishing, {{ISBN|978-1-4728-0067-1}}</ref>
* 10 September: Three destroyers found a convoy of invasion transports off Ostend and sank an escort vessel, two trawlers that were towing barges and one large barge.<ref name="Jackson"/>
* 13 September: Three destroyers sent to bombard Ostend but the operation was cancelled due to bad weather. A further twelve destroyers swept parts of the French coast between Roches Douvres, Cherbourg, Boulogne and Cape Griz Nez.<ref>{{cite web |url=https://www.naval-history.net/xDKWW2-4009-22SEP01.htm |work=British and Other Navies in World War 2 Day-by-Day |author= Kindell, Don
|title=Naval Events, September 1940 (Part 1 of 2): Sunday 1st – Saturday 14th |access-date=3 April 2021}}</ref> while an RAF bombing raid destroyed 80 barges at Ostend.{{sfn|Hough|Richards|1990|p=293}}
* 15 September: Sergeant [[John Hannah (VC)|John Hannah]] gained the [[Victoria Cross]] during a raid by RAF bombers on invasion barges at [[Antwerp]];{{sfn|Hough|Richards|1990|p=293}} four transport ships were damaged.{{sfn|Schenk|1990|p=348}}
* 17 September: A major attack by Bomber Command on ports along the occupied coast. 84 barges were damaged at Dunkirk.<ref name= "Jackson"/>
* 26 September: [[Operation Lucid]], a plan to send [[fire ship]]s into the harbours at Calais and Boulogne to destroy invasion barges, was abandoned when {{ship|RFA|War Nizam||2}}, one of the old [[tanker (ship)|tankers]] that were to be used, had engine failure and the other {{ship|RFA|War Nawab||2}} was suffering so many leaks that she was unfit for sea.{{sfn|Smith|1985|pp=104–105}}<ref>{{Cite web|url=http://www.naval-history.net/xDKWW2-4009-22SEP02.htm|title=Battle of Britain, September 1940|website=www.naval-history.net|access-date=2016-10-13|archive-url=https://web.archive.org/web/20160610154833/http://www.naval-history.net/xDKWW2-4009-22SEP02.htm|archive-date=10 June 2016}}</ref>
* 30 September: The [[Monitor (warship)|monitor]] {{HMS|Erebus|I02|6}} fired seventeen [[BL 15-inch Mk I naval gun|15-inch shells]] onto Calais docks.<ref name= "Jackson"/>
* 4 October: Second attempt at Operation Lucid, this time cancelled because of bad weather.{{sfn|Smith|1985|pp=106–107}}<ref name=navalhistoryoct40>{{cite web |url=https://www.naval-history.net/xDKWW2-4010-23OCT01.htm
|work=British and Other Navies in World War 2 Day-by-Day |author= Kindell, Don |title=Naval Events, October 1940 |access-date=3 April 2021}}</ref>
* 7 October: Third attempt at Lucid, cancelled when {{HMS|Hambledon|L37|6}}, the destroyer carrying the force commander, hit a mine and had to be towed home.{{sfn|Smith|1985|p=107}}<ref name=navalhistoryoct40/>
* 10–11 October: Operation Medium, the bombardment of invasion transports in Cherbourg. A concentrated RAF bombing raid during the night occupied the attention of German defences, allowing a Navy task force to approach to within gun range without detection. During the 18-minute bombardment, 120 15-inch shells were fired by the battleship [[HMS Revenge (06)|HMS ''Revenge'']], and a total of 801 [[QF 4.7-inch Mk IX & XII naval gun|4.7-inch shells]] were fired by her escorting destroyers. German [[coastal artillery]] replied for 30 minutes without hitting any of the warships.<ref name= "Revenge"/>
Between 15 July and 21 September, German sources stated that 21 transport vessels and 214 barges had been damaged by British air raids. These figures may have been under-reported.<ref name= "Jackson"/>
==The threat recedes==
Churchill was at times personally pessimistic about Britain's chances for victory, telling [[Hastings Ismay]] on 12 June 1940 that "[y]ou and I will be dead in three months' time".<ref name="reynolds1993">{{cite book | title=Churchill | publisher=Clarendon Press | author=Reynolds, David | year=1993 | location=Oxford | pages=249, 252, 254–255 | chapter = Churchill in 1940: The Worst and Finest Hour |editor1=Blake, Robert B. |editor2=Louis, William Roger | isbn=0-19-820626-7}}</ref> In mid-1940, an invasion attempt could have occurred at any time, but some times were more likely than others: The [[high tide]],<ref name="sptimes19400803">{{cite news | url=https://news.google.com/newspapers?id=Dk8wAAAAIBAJ&pg=5186%2C219407 | title=Next Week May See Nazis Attempt British Invasion | work=The St. Petersburg Times| date=3 August 1940 | access-date=26 November 2011 | page=1}}</ref> the phase of the moon and, most of all, the weather were considerations. The weather usually deteriorates significantly after September, but an October landing was not out of the question.{{cn|date=November 2023}} On 3 October, General Brooke wrote in his diary: "Still no invasion! I am beginning to think that the Germans may after all not attempt it. And yet! I have the horrid thought that he may still bring off some surprise on us."{{sfn|Alanbrooke|2001|loc=Entry 3 October 1940}}
The Battle of Britain had been won, and on 12 October 1940, unknown to the British, Hitler rescheduled Sea Lion for early 1941. By then, the state of Britain's defences had much improved, with many more trained and equipped men becoming available and field fortifications reaching a high state of readiness. With national confidence rising, Prime Minister Churchill was able to say: "We are waiting for the long promised invasion. So are the fishes&nbsp;..."<ref>{{cite web | title=Dieu Protege la France, Broadcast 21 October 1940 | work=The Churchill Society, London | url=http://www.churchill-society-london.org.uk/LaFrance.html | access-date=7 August 2006 | archive-date=12 May 2021 | archive-url=https://web.archive.org/web/20210512121529/http://www.churchill-society-london.org.uk/LaFrance.html }}</ref>
When [[Operation Barbarossa|Germany invaded the Soviet Union]], on 22 June 1941, it came to be seen as unlikely that there would be any attempted landing as long as that conflict was undecided{{spaced en dash}}from the British point of view at the time, the matter hung in the balance. In July 1941, construction of field fortifications was greatly reduced and concentration given to the possibility of a raid in force rather than a full-scale invasion.<ref>{{Cite web |title=Operation Barbarossa {{!}} History, Summary, Combatants, Casualties, & Facts {{!}} Britannica |url=https://www.britannica.com/event/Operation-Barbarossa |access-date=2023-01-12 |website=www.britannica.com |language=en}}</ref>
On 7 December 1941, a [[Imperial Japanese Navy#Aircraft carriers|Japanese carrier fleet]] launched a [[Attack on Pearl Harbor|surprise air attack on the American fleet at Pearl Harbor]]; the [[United States declaration of war upon Germany (1941)|United States entered the war]] on Britain's side. With America's ''[[Germany first]]'' strategic policy, resources flooded into the UK, effectively ending the danger of invasion after two years.<ref>{{Cite web |title=Digital History |url=https://www.digitalhistory.uh.edu/disp_textbook.cfm?smtID=3&psid=1408 |access-date=2023-01-12 |website=www.digitalhistory.uh.edu}}</ref>
In 1944, the British Army retained an "abnormally large force of over 100,000 men for defence of the United Kingdom and other contingencies which could have been used in Normandy" according to American historian [[Carlo D'Este|Carlo d'Este]].{{sfn|Beevor|2009|p=263}}
==Effectiveness==
General Brooke frequently confided his concerns to his private diary. When published, he included additional annotations written many years later:
{{blockquote|...&nbsp;I considered the invasion a very real and probable threat and one for which the land forces at my disposal fell far short of what I felt was required to provide any degree of real confidence in our power to defend these shores. It should not be construed that I considered our position a helpless one in the case of an invasion. Far from it. We should certainly have a desperate struggle and the future might well have hung in the balance, but I certainly felt that given a fair share of the fortunes of war we should certainly succeed in finally defending these shores. It must be remembered that if my diary occasionally gave vent to some of the doubts which the heavy responsibility generated, this diary was the one and only outlet for such doubts.{{sfn|Alanbrooke|2001|loc=Entry 15 September 1940}} }}
The question of whether the defences would have been effective in invasion is vexed. In mid-1940, the preparations relied heavily upon field fortifications. The First World War made it clear that assaulting prepared defences with infantry was deadly and difficult, but similar preparations in Belgium had been overrun by well-equipped German Panzer divisions in the early weeks of 1940 and with so many armaments left at Dunkirk, British forces were woefully ill-equipped to take on German armour. On the other hand, while British preparations for defence were ''ad hoc'', so were the German invasion plans: a fleet of 2,000 converted barges and other vessels had been hurriedly made available and their fitness was debatable; in any case, the Germans could not land troops with all their heavy equipment. Until the Germans captured a port, ''both'' armies would have been short of tanks and heavy guns.{{sfn|MacKenzie|1995|p=180}}
The later experiences of the Canadian Army during the disastrous [[Dieppe Raid]] of 1942, American forces on [[Omaha Beach]] on [[Normandy Landings|D-Day]] and taking on [[Empire of Japan|Japanese]] defenders on [[Pacific Islands]] showed that, under the right conditions, a defender could exact a terrible price from assaulting forces, significantly depleting and delaying enemy forces until reinforcements could be deployed to appropriate places via the sea and inland.<ref>{{Cite web |last=Granatstein |first=Jack |date=May 29, 2014 |title=Dieppe: A Colossal Blunder |url=https://www.canadashistory.ca/explore/military-war/dieppe-a-colossal-blunder |access-date=January 12, 2023 |website=www.canadashistory.ca}}</ref>
In the event of invasion, the Royal Navy would have sailed to the landing places, possibly taking several days. The German Kriegsmarine had, however, been severely depleted by the Norwegian campaign. It lost a heavy cruiser, a light cruiser, and almost a quarter of its destroyers; two heavy units, a [[Deutschland-class cruiser|Panzerschiff]] and a battlecruiser, were out of action due to torpedo damage. In late 1940, the Kriegsmarine was thus virtually bereft of heavy units to either provide gunfire support to a landing or to counter any intervention by the Royal Navy. It is now known that the Germans planned to land on the southern coast of England; one reason for this site was that the narrow seas of the [[English Channel]] could be blocked with [[naval mine|mines]], [[submarine]]s and [[torpedo boat]]s and thus prevent the Royal Navy from defending against an invasion. While German naval forces and the Luftwaffe could have extracted a high price from a defending Royal Navy, they could not have hoped to prevent interference with attempts to land a second wave of troops and supplies that would have been essential to German success{{spaced en dash}}even if, by then, the Germans had captured a port essential for bringing in significant heavy equipment. In this scenario, British land forces would have faced the Germans on more equal terms than otherwise and it was only necessary to delay the German advance, preventing a collapse until the German land forces were, at least temporarily, isolated by the Royal Navy and then mounting a counterattack.{{sfn|James|2006|pp=38–40}}
Scholarly consideration of the likely outcome of invasion, including [[Operation Sea Lion (wargame)|the 1974 Royal Military Academy Sandhurst war game]],<ref>{{cite web | title=Operation Sealion&nbsp;– summary of an exercise held at the Staff College | work=Sandhurst in 1974 | url=http://mr-home.staff.shef.ac.uk/hobbies/seelowe.txt | access-date=1 June 2006 | archive-date=13 June 2008 | archive-url=https://web.archive.org/web/20080613114509/http://mr-home.staff.shef.ac.uk/hobbies/seelowe.txt }}</ref> agree that while German forces would have been able to land and gain a significant [[beachhead]], intervention of the Royal Navy would have been decisive and, even with the most optimistic assumptions, the German army would not have penetrated further than [[GHQ Line]] and would have been defeated.<ref>{{cite web | title=Why Sealion is not an option for Hitler to win the war | author=Alison Brooks | work=essay | url=http://www.philm.demon.co.uk/Miscellaneous/Sealion.htm | access-date=16 July 2012 | archive-date=13 July 2012 | archive-url=https://web.archive.org/web/20120713051851/http://www.philm.demon.co.uk/Miscellaneous/Sealion.htm }}<br />{{cite web|title=Why Operation Sealion Wouldn't Work |work=essay |url=http://www.alternatehistory.com/gateway/essays/Sealion.html |access-date=16 July 2012 |archive-url=https://web.archive.org/web/20120104112946/http://www.alternatehistory.com/gateway/essays/Sealion.html |archive-date=4 January 2012 }}<br />{{cite web | title=Sea Lion vs. Overlord | author=Larry Parker | url=http://www.globeatwar.com/article/sea-lion-vs-overlord | access-date=8 April 2020}}<br />Evans, 2004, the outcome is a major theme of this work, Evans gives emphasis to German logistical problems.</ref>{{sfn|Gatchel|1996|pp=35–38}}
Following the failure to gain even local air superiority in the Battle of Britain, Operation Sea Lion was postponed indefinitely. Hitler and his generals were aware of the problems of an invasion. Hitler was not ideologically committed to a long war with Britain and many commentators suggest that German invasion plans were a feint never to be put into action.{{sfn|Liddell Hart| 1958| pp= 126–127}}
While Britain may have been militarily secure in 1940, both sides were aware of the possibility of a political collapse. If the Germans had won the Battle of Britain, the Luftwaffe would have been able to strike anywhere in southern England and with the prospect of an invasion, the British government would have come under pressure to come to terms: the extensive anti-invasion preparations demonstrated to Germany and to the people of Britain that whatever happened in the air, the United Kingdom was both able and willing to defend itself.{{sfn|MacKenzie|1995|pp=180–184}}
==See also==
{{Portal|United Kingdom}}
* [[Coats Mission]]
* [[Eastbourne Redoubt]], home of the Combined Service Museum
* [[Dymchurch Redoubt]]
* [[Operation Lucid]]
* [[Atlantic Wall]]
* [[British County Divisions]], regular infantry divisions raised for static and coastal defence duties
==References==
===Footnotes===
{{Reflist|group="nb"}}
===Notes===
{{Reflist}}
===General references===
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| last        = Alanbrooke
| year        = 2001
| first       = Field Marshal Lord
| author-link = Alan Brooke, 1st Viscount Alanbrooke
| title       = War Diaries 1939–1945
| publisher   = Phoenix Press
| isbn        = 1-84212-526-5
}}
* {{cite book
| title       = Fighting Nazi Occupation: British Resistance 1939–1945
| last        = Atkin
| first       = Malcolm
| publisher   = Pen and Sword
| year        = 2015
| isbn        = 978-1-4738-3377-7
| location    = Barnsley
}}
* {{cite book
| last        = Banks
| year        = 1946
| first       = Sir Donald
| author-link = Donald Banks
| title       = Flame Over Britain
| publisher   = Sampson Low, Marston and Co
| oclc        = 1043980996
}}
* {{cite book
| last        = Barclay
| year        = 2013
| first       = Gordon
| title       = If Hitler Comes: Preparing for Invasion: Scotland 1940
| url         = https://books.google.com/books?id=VbG8BQAAQBAJ&pg=PP1
| publisher   = Birlinn Ltd
| isbn        = 978-1-84341-062-1
}}
* {{cite book
| last        = Beevor
| first       = Antony
| author-link = Antony Beevor
| title       = D-Day: The Battle for Normandy
| publisher   = Viking
| date        = 2009
| location    = London
| isbn        = 978-0-670-88703-3 }}
* {{cite journal
| last1       = Bennett
| first1      = A.
| title       = Work of the Essex County Council Archaeology Section, 1997
| journal     = Essex Archaeology and History
| date        = 1998
| volume      = 29
| pages       = 183–193
| url         = http://esah1852.org.uk/images/pdf/third-series/T3290000.pdf
| issn        = 0308-3462
}}
* {{cite book
| last        = Cameron
| year        = 2006
| first       = A Bryce
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| publisher   = Trafford Publishing
| isbn        = 1-55212-319-7
}}
* {{cite book
| last        = Churchill
| orig-date   = 1949
| first       = Winston
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| title       = Their Finest Hour
| publisher   = Penguin
| series      = The Second World War
| volume      = II
| isbn        = 0-14-144173-9
| year        = 2005
| ref         = {{SfnRef|Churchill|1949}}
}}
* {{cite book
| last1       = Churchill
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| last2       = Gilbert
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| title       = Winston S. Churchill: Finest hour, 1939-1941
| date        = 1983
| publisher   = Houghton Mifflin
| location    = Boston
| isbn        = 978-0-395-34402-6
| url         = https://books.google.com/books?id=k0omAQAAMAAJ
| language    = en
}}
* {{cite book
| last        = Churchill
| first       = Winston
| title       = Memoirs of The Second World War
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}}
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| type        = PhD thesis
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}}
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| year        = 1957
| location    = London
| publisher   = HMSO
| oclc        = 491400913
}}
* {{cite book
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| year        = 1974
| first       = Richard
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}}
* {{cite book
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| url-access  = registration
| url         = https://archive.org/details/invasiondefendin0000crui
}}
* {{cite book
| year        = 1962
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| location    = Washington, DC
| publisher   = GPO
| oclc        = 985120608
}}
* {{cite book
| last        = Edgerton
| year        = 2012
| first       = David
| title       = Britain's War Machine: Weapons, Resources and Experts in the Second World War
| publisher   = Penguin
| isbn        = 978-0-14-102610-7
}}
* {{cite book
| last        = Evans
| year        = 2004
| first       = Martin Marix
| title       = Invasion! Operation Sealion 1940
| publisher   = Longman
| isbn        = 0-582-77294-X
}}
* {{cite book
| last        = Fleming
| first       = Peter
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| title       = Invasion 1940
| publisher   = Rupert Hart-Davis
| year        = 1957
| oclc        = 249944008
}}
* {{cite book
| last        = Foot
| year        = 2006
| first       = William
| title       = Beaches, Fields, Streets, and Hills&nbsp;... the Anti-invasion Landscapes of England, 1940
| publisher   = Council for British Archaeology
| isbn        = 1-902771-53-2
}}
* {{cite book
| last        = Gatchel
| year        = 1996
| first       = Theodore L.
| title       = At the Water's Edge: Defending Against the Modern Amphibious Assault
| publisher   = Naval Institute Press
| isbn        = 978-1-55750-308-4
}}
* {{cite book
| last        = Gillies
| year        = 2006
| first       = Midge
| author-link = Midge Gillies
| title       = Waiting for Hitler&nbsp;– Voices from Britain on the Brink of Invasion
| publisher   = Hodder & Stoughton
| isbn        = 0-340-83798-5
}}
* {{cite book
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| last2       = Waldren
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| title       = London's Armed Police: 1829 to the Present
| date        = 1986
| publisher   = Arms and Armour Press
| location    = London
| isbn        = 978-0-85368-880-8
| url         = https://books.google.com/books?id=t_wEAQAAIAAJ
| language    = en
}}
* {{cite book
| last        = Hayward
| year        = 2001
| first       = James
| author-link = James Hayward (writer)
| title       = The Bodies On The Beach&nbsp;– Sealion, Shingle Street and the Burning Sea Myth of 1940
| publisher   = CD41 Publishing
| isbn        = 0-9540549-0-3
}}
* {{cite book
| last        = Hewitt
| first       = Geoff
| year        = 2008
| title       = Hitler's Armada: The Royal Navy and the Defence of Great Britain, April–October 1940
| publisher   = Pen & Sword Maritime
| isbn        = 978-1-84415-785-3
}}
* {{cite book
| last1       = Hough
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| title       = The Battle of Britain
| year        = 1990
| orig-date   = 1989
| publisher   = Coronet
| isbn        = 0-340-53470-2
}}
* {{cite book
| last1       = Hylton
| first1      = Stuart
| title       = Kent and Sussex 1940: Britain's frontline
| date        = 2004
| publisher   = Leo Cooper
| location    = Barnsley
| isbn        = 978-1-84415-084-7
| url         = https://books.google.com/books?id=0tSXAwAAQBAJ
| language=en
}}
* {{cite journal
| last        = James
| date        = September 2006
| first       = Brian
| title       = Pie in the Sky
| url         = https://www.historytoday.com/archive/pie-sky
| volume      = 56
| issue       = 9
| journal     = [[History Today]]
}}
* {{cite book
| last        = Liddell Hart
| year        = 1958
| first       = Basil
| author-link = Basil Liddell Hart
| title       = The German Generals Talk
| publisher   = Berkley Publishing
| orig-date   = 1948
| oclc = 855386423
}}
* {{cite book
| last        = Long
| first       = Gavin
| author-link = Gavin Long
| title       = To Benghazi
| year        = 1952
| series      = Australia in the War of 1939–1945. Series 1&nbsp;– Army
| volume      = I
| publisher   = Australian War Memorial
| url         = https://www.awm.gov.au/collection/RCDIG1070200/
| location    = Canberra
| oclc        = 18400892
}}
* {{cite book
| last        = Lowry
| year        = 2004
| first       = Bernard
| title       = British Home Defences 1940–45
| publisher   = Osprey Publishing
| isbn        = 1-84176-767-0
}}
* {{cite book
| last        = Mace
| date        = July 2001
| first       = Martin
| title       = Vehicles of the Home Guard
| publisher   = Historic Military Press
| isbn        = 1-901313-08-5
}}
* {{cite book
| last        = MacKenzie
| year        = 1995
| first       = S. P.
| title       = The Home Guard&nbsp;– A Military and Political History
| publisher   = Oxford University Press
| isbn        = 0-19-820577-5
}}
* {{cite book
| last1       = Manchester
| first1      = William
| last2       = Reid
| first2      = Paul
| title       = The Last Lion: Winston Spencer Churchill / Defender of the Realm: 1940–1965
| year        = 2012
| publisher   = Little, Brown and Company
| isbn        = 978-0-316-22214-3}}
* {{cite book
| last        = McClymont
| first       = W. G.
| year        = 1959
| title       = To Greece
| series      = Official History of New Zealand in the Second World War 1939-45
| location    = Wellington, New Zealand
| publisher   = War History Branch, [[Department of Internal Affairs (New Zealand)]]
| url         = http://nzetc.victoria.ac.nz/tm/scholarly/tei-WH2Gree.html
| access-date = 24 March 2021
| via         = New Zealand Electronic Text Collection
| oclc        = 1047868106
}}
* {{cite periodical
| url         = https://researchcentre.army.gov.au/sites/default/files/aaj_220_sep_1967.pdf
| title       = Sub-Machine Guns
| last        = Parker
| first       = A.
| periodical  = Australian Army Journal
| issue       = 220
| date        = September 1967
| oclc        = 85448187
| pages       = 25–43
}}
* {{cite book
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| first       = Matthew
| title       = The Battle of Britain: July – October 1940
| year        = 2000
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| isbn        = 0-7472-3452-3
}}
* {{cite book
| last        = Ray
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| title       = The Second World War: A Narrative History
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}}
* {{cite book
| last1       = Rowe
| first1      = Mark
| title       = Don't Panic: Britain Prepares for Invasion 1940
| date        = 2011
| publisher   = The History Press
| location    = Stroud
| isbn        = 978-0-7524-7612-4
| url         = https://books.google.com/books?id=8VI7AwAAQBAJ
| language    = en
}}
* {{cite book
| last       = Ruddy
| year       = 2003
| first      = Austin
| title      = British Anti-Invasion Defences 1940–1945
| publisher  = Historic Military Press
| isbn       = 1-901313-20-4
}}
* {{cite book
| last        = Schenk
| first       = Peter
| date        = 1990
| title       = Invasion of England 1940: The Planning of Operation Sealion
| location    = London
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| isbn        = 0-85177-548-9
}}
* {{cite book
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| title       = Aftermath: readings in the archaeology of recent conflict
| date        = 2009
| publisher   = Springer
| location    = New York
| isbn        = 978-0-387-88521-6
| url         = https://books.google.com/books?id=XMqSBKRkjy8C
| language    = en
}}
* {{cite book
| last        = Smith
| first       = Peter C.
| author-link = Peter C. Smith
| title       = HMS Wild Swan
| year        = 1985
| location    = London
| publisher   = William Kimber
| isbn        = 0-7183-0542-6
}}
* {{cite book
| last        = Stevens
| first       = W. G.
| year        = 1958
| title       = Problems of 2 NZEF
| series      = Official History of New Zealand in the Second World War 1939–45
| location    = Wellington, New Zealand
| publisher   = War History Branch, Department of Internal Affairs
| url         = http://nzetc.victoria.ac.nz/tm/scholarly/tei-WH2Prob.html
| via         = New Zealand Electronic Text Collection
| access-date = 24 March 2021
| oclc        = 846901610
}}
* {{cite book
| last1       = Storey
| first1      = Neil R.
| title       = Beating the Nazi Invader Hitler's Spies, Saboteurs and Secrets in Britain 1940
| date        = 2020
| publisher   = Pen & Sword Books Limited
| location    = Havertown
| isbn        = 978-1-5267-7297-8
| url         = https://books.google.com/books?id=iS8NEAAAQBAJ
| language    = en
}}
* {{cite book
| last1       = Thompson
| first1      = Julian
| title       = Dunkirk: Retreat to Victory
| date        = 2009
| publisher   = Pan Macmillan
| location    = New York
| isbn        = 978-0-330-50845-2
| url         = https://books.google.com/books?id=gdRW9HZe-UwC
| access-date = 29 March 2021
| language    = en
}}
* {{cite book
| last1       = Todman
| first1      = Daniel
| title       = Britain's war. Into battle, 1937-1941
| date        = 2016
| publisher   = Oxford University Press
| location    = Oxford
| isbn        = 978-0-19-062180-3
| url         = https://books.google.com/books?id=qzHKDAAAQBAJ
| language    = en
}}
* {{cite book
| last        = Ward
| year        = 1997
| first       = Arthur
| title       = Resisting the Nazi Invader
| publisher   = Constable and Co
| isbn        = 0-09-476750-5
}}
* {{cite book
| last1       = Warner
| first1      = Philip
| title       = Invasion Road
| date        = 1980
| publisher   = Cassell
| location    = London
| isbn        = 0-304-30543-X
}}
* {{cite book
| last        = White
| year        = 1955
| first       = John Baker
| author-link = John Baker White (British politician)
| title       = The Big Lie
| publisher   = Evans Brothers
| oclc        = 874233110
}}
* {{cite book
| last        = Wills
| year        = 1985
| first       = Henry
| author-link = Henry Wills (writer)
| title       = Pillboxes: A Study of UK Defences
| publisher   = Leo Cooper
| isbn        = 0-436-57360-1
}}
===Official documents===
* ''Consolidated Instructions to Invasion Committees in England and Wales'' (July 1942) HM Government. {{oclc|1114844015}}
* {{Cite book
| title      = Barrel Flame Traps, Flame Warfare
| publisher  = [[War Office]]
| series     = Military Training Pamphlet No. 53. Part 1
| date       = July 1942
| oclc       = 67270997
}}
===Collections===
* {{cite web
| url        = http://www.nationalarchives.gov.uk
| title      = The National Archives
| access-date = 3 August 2010
| work       = Repository of UK government records
}}
* {{cite web
| url        = http://www.bbc.co.uk/ww2peopleswar/
| title      = WW2 People's War
| access-date = 3 August 2010
| publisher  = BBC
}}&nbsp;– an online archive of wartime memories contributed by members of the public and gathered by the BBC.
* {{cite news
| url        = http://archive.timesonline.co.uk/tol/archive/
| archive-url = https://web.archive.org/web/20080903140039/http://archive.timesonline.co.uk/tol/archive/
| url-status = dead
| archive-date = 3 September 2008
| title      = The Times and The Sunday Times Archive
| access-date = 3 August 2010
| location   = London
| first1     = Rachel
| last1      = Sylvester
| first2     = Sam
| last2      = Coates
}}&nbsp;– subscription required
== Further reading ==
* Bird, C. ''Silent Sentinels&nbsp;– A study of the fixed defences constructed in Norfolk during WWI and WWII'' (Dereham: The Larks Press 1999) {{ISBN|0-948400-81-1}}
* {{Cite book
| last       = Butler
| year       = 1957
| first      = J R M
| author-link = James Ramsay Montagu Butler
| title      = Grand Strategy Volume II September 1939 – June 1941
| publisher  = Her Majesty's Stationery Office
| orig-date   = 1975
| asin       = B0043KQ3W2
}}
* {{Cite book
| last       = Cullen
| year       = 2011
| first      = Stephen
| title      = In Search of the Real Dad's Army; The Home Guard and the Defence of the United Kingdom, 1940–1944
| publisher  = Pen and Sword
| isbn       = 978-1-84884-269-4
}}
* Foot, William. ''The Battlefields That Nearly Were. Defended England 1940'' (Stroud: Tempus Publishing 2006) {{ISBN|978-0-7524-3849-8}}
* Kauffmann, J.E. and Jurga, Robert M. ''Fortress Europe: European Fortifications of World War II'', Da Capo Press, 2002. {{ISBN|0-306-81174-X}}
* {{Cite book
| last       = Lampe
| year       = 2007
| first      = David
| title      = The Last Ditch: Britain's Resistance Plans Against the Nazis
| publisher  = Greenhill Books
| isbn = 978-1-85367-730-4
}}
* {{Cite book
| last       = Longmate
| year       = 2004
| first      = Norman
| author-link = Norman Longmate
| title      = If Britain Had Fallen
| publisher  = Greenhill Books
| isbn       = 978-1-85367-599-7
| orig-date   = 1972
}}
* {{Cite book
| last       = Macksey
| year       = 1999
| first      = Kenneth
| author-link = Kenneth Macksey
| title      = Invasion: Alternative History of the German Invasion of England, July 1940
| publisher  = Greenhill Books
| orig-date   = 1980
| isbn       = 978-1-85367-361-0
}}
* {{Cite book
| last       = Osborne
| year       = 2004
| first      = Mike
| title      = Defending Britain&nbsp;... Twentieth Century Military Structures in the Landscape
| publisher  = Tempus Publishing
| isbn       = 0-7524-3134-X
}}
* Osborne, Mike. ''20th Century Defences in Britain'' (Stroud: Tempus Publishing 2003) {{ISBN|0-9540378-1-2}}
* Ross, Stewart. ''World War II Britain. History from Buildings'' (London: Franklin Watts 2006) {{ISBN|0-7496-6468-1}}
==External links==
{{Commons category|World War II home defence of the United Kingdom}}
* [https://www.bbc.co.uk/history/worldwars/wwtwo/invasion_ww2_01.shtml The German Threat to Britain in World War Two.] By [[Dan Cruickshank]] BBC
* [https://web.archive.org/web/20150923215249/http://www.diverse.tv/programme/The-Real-Dads-Army-2945.html?filter=type_ ''The Real Dad's Army'']&nbsp;– TV documentary
* [http://news.bbc.co.uk/1/hi/england/kent/4982116.stm Churchill's mysterious map]
* [http://www.pillboxesuk.co.uk/ Pillboxesuk.co.uk]
* [http://ads.ahds.ac.uk/catalogue/specColl/dob/index.cfm Defence of Britain database] {{Webarchive|url=https://web.archive.org/web/20110515212439/http://ads.ahds.ac.uk/catalogue/specColl/dob/index.cfm |date=15 May 2011 }}
* {{Coord|54|0|13|N|2|32|52|W|region:GB_type:landmark|name=Centre of Great Britain}} Landmarks centre of Great Britain
{{Fortifications}}
{{DEFAULTSORT:British Anti-Invasion Preparations Of World War Ii}}
[[Category:1940 in military history]]
[[Category:1941 in military history]]
[[Category:1940 in the United Kingdom]]
[[Category:1941 in the United Kingdom]]
[[Category:Battle of Britain]]
[[Category:British World War II defensive lines]]
[[Category:Invasions of the United Kingdom]]
[[Category:Military history of the United Kingdom during World War II]]
[[Category:United Kingdom home front during World War II]]