British anti-invasion preparations of the Second World War

British anti-invasion preparations of the Second World War entailed a large-scale division of military and civilian mobilisation in response to the threat of invasion (Operation Sea Lion) by German armed forces in 1940 and 1941.

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, whose main responsibility was to reinforce the BEF in France, had very limited resources available, with six poorly trained and equipped Territorial Army divisions in England, two in Scotland and three more in reserve.

VII Corps was based at Headley Court in Surrey to the south of London and comprised 1st Armoured and 1st Canadian Divisions with the 1st Army Tank Brigade.

[23] 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.

[35] Whatever was left of the RAF would have been committed to intercepting the invasion fleet in concert with the Royal Navy[36] – to fly in the presence of an enemy that enjoys air superiority is very dangerous.

[47] 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.

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.

[83][84] Pimples, popularly known as 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.

Many of these fortifications were specified by the Air Ministry and defensive designs were unique to airfields – 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 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.

[117] Other basic defensive measures included the removal of signposts, milestones (some had the carved details obscured with cement) and railway station signs, making it more likely that an enemy would become confused.

[123] 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 – generally meaning by parachutists – was in progress.

[130] Instructions to the invasion committees stated: "... 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.

[134] 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.

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.

[136][137] 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.

[157][158] 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.

A young member of the Home Guard (LDV) recalled: 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.

For occasions where time did not permit the passing of cables and chains we had concrete cylinders the size of a 45 gallon oil or tar barrel ready to roll into a roadway or other gap.

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.

The interrogation of a Luftwaffe pilot revealed the existence of such weapons was common knowledge,[172] and documents found after the war showed the German high command were deceived.

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.

[181] 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.

[182] The 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.

[184] Some notable operations are shown below: Between 15 July and 21 September, German sources stated that 21 transport vessels and 214 barges had been damaged by British air raids.

So are the fishes ..."[198] When 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 – from the British point of view at the time, the matter hung in the balance.

[200] 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.

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 mines, submarines and torpedo boats and thus prevent the Royal Navy from defending against an invasion.