British anti-invasion preparations of the Second World War

Detail from a pillbox embrasure.

British anti-invasion preparations of World War II entailed a large scale programme of military and civilian mobilisation in response to the threat of invasion by German armed forces in 1940 and 1941. The army needed to recover from the defeat of the British Expeditionary Force in France and one and a half million men were enrolled as part-time soldiers in the Home Guard. The rapid construction of field fortifications transformed much of Britain, especially southern England, into a prehpared battlefield. Short of heavy weapons and equipment, the British had to make the best use of whatever was available.

The German invasion plan, known to English speakers as Operation Sealion, was never taken beyond the preliminary assembly of forces stage. Today, very little remains of Britain's anti-invasion preparations. Only reinforced concrete structures such as pillboxes are common and even these have, until very recently, been unappreciated as historical monuments.

Political and military background

On 1 September 1939, Germany invaded Poland; two days later, Britain and France declared war on Germany, launching the European aspect of World War II. Within three weeks, the Red Army of the Soviet Union invaded the eastern regions of Poland in fulfillment of a secret pact with Nazi Germany. A British Expeditionary Force (BEF) was sent to the Franco-Belgian border, but Britain and France would not take any direct action in support of the Poles. By 1 October, Poland was completely overrun.

There was little fighting over the months that followed. In a period known as the Phoney War, French and British soldiers trained for war and constructed and manned defenses on the eastern borders of France.

On 9 April 1940, Germany invaded Denmark and Norway. This operation preempted Britain's intention to invade Norway first. Denmark surrendered immediately, and, after fierce fighting, 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.

On 7 May and 8 May 1940 in the British House of Commons, the Norway Debate revealed intense dissatisfaction with and outright hostility towards the government of Prime Minister Neville Chamberlain. Two days later, with events moving swiftly, Chamberlain resigned and was succeeded by Winston Churchill.

On 10 May 1940, Germany invaded France. By that time, the BEF consisted of ten infantry divisions in three corps, a tank brigade and a RAF detachment of around 500 aircraft. The BEF was pinned by a German diversionary attack through Belgium and then isolated by the main attack that came through the Ardennes forest. Well equipped and highly mobile Panzer divisions of the Wehrmacht easily overran the prepared defenses, another painful lesson. There was some fierce fighting, but most of the BEF withdrew to a small area around the French port of Dunkirk.

As things had gone badly for the allies in France, it became evident that some thought needed to be given to the possibility of having to resist an attempted invasion of Britain by German forces.

British armed forces

British Army

British prisoners at Dunkirk, France, June 1940.

The evacuation of British and French forces (Operation Dynamo) began on 26 May with air cover provided by the RAF at heavy cost. Over the following ten days, 338,226 French and British soldiers were 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. Some soldiers returned even without their rifles.

In June 1940, the British Army had 22 infantry divisions and one armoured division. The infantry divisions were, on average, at half strength, had only one-sixth of their normal artillery, and were almost totally lacking in transport. There was a critical shortage of ammunition such that none could be spared for practice. VII Corps was formed to control the Home Forces' general reserve, and included the 1st Armoured Division.

Home Guard

British Home Guard improvised weapons

Main article: British Home Guard

On 14 May 1940, Secretary of State for War, Anthony Eden, announced the creation of the Local Defence Volunteers (LDV) — later to become known as the Home Guard. The announcement was met with enthusiasm and far more men volunteered than the government expected; by the end of June, there were nearly 1.5 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 whatever was available: guns in private ownership, a knife or bayonet on a pole, Molotov cocktails and improvised flame throwers.

Standard Mk II Beaverette II light reconnaissance cars manned by members of the Home Guard in the Highlands of Scotland, 14 February 1941.

By July 1940, the situation had improved somewhat with uniforms, a modicum of training and the arrival of hundreds of thousands of rifles and millions of rounds of ammunition from the USA. 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 inflammable material of which more than six million were made), and the No. 73 Grenade (an anti-tank grenade resembling a Thermos flask).

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 — thumped against the target with sufficient force to stick — 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 its distribution in large numbers until early 1941, and in the end, it is likely that fewer than 250,000 were produced.

A measure of mobility was provided by bicycles, motorcycles, private vehicles and horses. A small number of 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.

Later in 1941, more sophisticated weapons were made available such as the Blacker Bombard anti-tank weapon, the Northover Projector (a black powder powered mortar), and the Smith Gun (a small artillery gun that could be towed by a private motorcar).

Royal Air Force

Main article: Battle of Britain

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.

If the German air force had prevailed and a landing attempted, a much-reduced Royal Air Force would have been obliged to operate from airfields well away from the south east 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. Whatever was left of the RAF would have been committed to intercepting the invasion fleet in concert with the Royal Navy — 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.

Every available aircraft was to be committed to the defence. In the event of invasion almost anything that was not a fighter would be converted to a bomber — student pilots, some in the very earliest stages of training, would use around 350 Tiger Moth and Magister trainers to drop 20 lb bombs from rudimentary bomb racks.

Shortly before the outbreak of World War II the Chain Home radar system began to be installed in the south of England, resulting in three radar stations being operational by 1937. Although the German High Command suspected that the British may have been developing these systems, Zeppelin test flights had proved inconclusive. As a result the expanding Chain Home radar system, and aircraft-based radar first fielded in 1940, became a vital piece of Britain's defensive capabilities during the Battle of Britain.

Royal Navy

The British Home Fleet was a force that dwarfed anything the Kriegsmarine could put to sea. On 1 July, there were one cruiser and 23 destroyers committed to escort duties in the Western Approaches. Also committed to escort duties were 12 destroyers and one cruiser on the Tyne and the aircraft carrier Argus. More immediately available were a total of 10 destroyers on the south coast ports of Dover and Portsmouth, a cruiser and 3 destroyers at Sheerness on the River Thames, 3 cruisers and 7 destroyers at the Humber, 9 destroyers at Harwich, and another two cruisers at Rosyth. The rest of the Home Fleet comprising 5 battleships, 3 cruisers, and 9 destroyers were based far to the north at Scapa Flow. There were, in addition, many corvettes, minesweepers, and other small vessels. 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.

Field fortifications

The British engaged upon an extensive programme of field fortification.

On 27 May 1940 a Home Defence Executive was formed under General Sir Edmund Ironside, Commander-in-Chief Home Forces to organise the defence of Britain. 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. The stop lines were designated Command, Corp and Divisional according to their status. The longest and most heavily fortified was the General Headquarters anti-tank line, GHQ Line, which ran across southern England, wrapped around London and then ran north to Yorkshire. It was intended to protect the national capital and the industrial heartland of England. Other major lines included the Taunton Stop Line which defended against an advance from England's south-west peninsula. London and other major cities were ringed with inner and outer stop lines. In all some 50 stop lines were constructed, although some were never completed.

Military thinking shifted rapidly. Given the lack of equipment and properly trained men, Ironside had 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.

However, Prime Minister Churchill was not satisfied with Ironside's progress especially with regard to the creation of a mobile reserve. The Secretary of State for War (Anthony Eden) suggested that Ironside should be replaced by General Brooke (later known as Lord Alanbrooke). On 17 July 1940 Churchill spent an afternoon with Brooke and was soon convinced that they were in close agreement as to how best to defend the nation and on 19 July Brooke replaced Ironside.

Brooke's appointment coincided with more trained men and better equipment becoming available. Under Brooke new strategies and tactics were devised. More concentration was placed on defending the coastal crust and inland a hedgehog defence strategy of defended localities and anti-tank islands was established, each having all-round defence. Many of these anti-tank islands were established along the already constructed stop lines where existing defences could be integrated into the new strategy and, especially, at towns and villages where there was a Home Guard to provide personnel.

Coastal crust

Coastal searchlight.

See also: Cross-Channel guns in the Second World War

It was understood that any German invasion of Britain would have to involve the landing of troops and equipment somewhere on the coast. The landings could take place anywhere, but the most vulnerable areas were the south and east coasts of England. Here, Emergency Coastal Batteries were constructed to protect ports and likely landing places. 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 inch (152 mm), 5.5 inch (140 mm), 4.7 inch (120 mm) and 4 inch (102 mm) guns. These had very little ammunition, sometimes as few as ten rounds apiece. At Dover, two 14 inch (356 mm) guns known as Winnie and Pooh were employed. Dover Castle had been a naval fort since World War I and had two 9.2 inch guns and four six inch guns after modernisation in the late 1920s. There were also a small number of land based torpedo launching sites.

Concertina wire.

Beaches were blocked with 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. The wire would also serve to demarcate extensive minefields 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.

Piers, ideal for landing of troops, and situated in large numbers along the South Coast of England, were disassembled, blocked or otherwise destroyed. Many piers were not immediately reconstructed or opened in the Post-War years and remained in their disabled state until the late 1940s or early 1950s.

Where a barrier to tanks was required, beach scaffolding (also known as Admiralty Scaffolding or obstacle Z1) was constructed. Essentially, this was a fence of scaffolding tubes 9 feet (3 m) high and was placed at low water so that tanks could not get a good run at it. Beach scaffolding was deployed along hundreds of miles of vulnerable beaches.

An even more robust barrier to tanks was provided by long lines of anti-tank cubes. The cubes were made of reinforced concrete 5 feet (1.5 m) to a side. Thousands were cast in situ in rows sometimes two or three deep.

Inchgarvie can be seen just below the Forth Bridge

The beaches themselves were overlooked by pillboxes of various types (see British hardened field defences of World War II). These were sometimes placed low down to get maximum advantage from 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.

Many small islands and peninsulas were fortified in order to provide protection for inlets and other strategic targets. At the Firth of Forth in East-Central Scotland, Inchgarvie Island was heavily fortified with several gun emplacements which can still be seen. This provided invaluable defence, not only from seaborne attacks against the bridge but also for nearby Rosyth Dockyard, approximately a mile upstream from the bridge. Further out towards the sea, Inchmickery Island, about 1.6 miles 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 Island also remain.

Lines and islands

A section of the river Wey incorporated into GHQ Line as an anti-tank barrier.

The primary purpose of the stop lines and the anti-tank islands that followed was to hold up the enemy, slowing his 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.

Thousands of miles of anti-tank ditches were dug, usually by mechanical excavators, but occasionally by hand. They were typically 18 feet (5.5 m) wide and 11 feet (3.4 m) deep and could be either trapezoidal or triangular in section with the defended side being especially steep and revetted with whatever material was available.

Anti-tank cubes.

Elsewhere, anti-tank barriers were made of massive reinforced concrete obstacles, either cubic or cylindrical. The cubes generally came in two sizes: 5 feet (1.5 m) or 3.5 feet (1 m) high. In a few places, anti-tank walls were constructed — essentially continuously abutted cubes.

Anti-tank cylinder.

Large cylinders were made from a section of sewer pipe 3–4 feet (90–120 cm) in diameter filled with concrete typically to a height of 4 to 5 feet, frequently with a dome at the top. Smaller cylinders cast from concrete are also frequently found.

Pimples, popularly known as Dragon's teeth, were pyramids of concrete 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 2 feet (60 cm) high and about 3 feet (90 cm) square at the base. There was also a conical form.

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.

Where natural anti-tank barriers only needed to be augmented, concrete or wooden posts would suffice.

Removable roadblock at a bridge on the Basingstoke Canal.

Roads offered the enemy fast routes to their objectives and consequently they were blocked at strategic points. Many of the roadblocks 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.

The simplest of the removable roadblocks consisted of concrete cylinders of various sizes but typically about 2 feet (60 cm) in diameter and 3 feet (1 m) high; these could be manhandled into position as required. However, these would be insufficient to stop armoured vehicles. One common type of removable anti-tank roadblock comprised massive concrete posts permanently installed at the roadside; these posts had holes and/or slots to accept horizontal railway lines or rolled steel joists (RSJs). Similar blocks were placed across railway tracks because tanks can move along tracks almost as easily as they can along roads. These blocks would be placed strategically where it was difficult for a vehicle to go around — anti-tank obstacles and mines being positioned as required — and they could be opened or closed within a matter of minutes.

Sockets for hedgehog removable roadblock on a bridge over the Kennet and Avon Canal.

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 hedgehog. The second type comprised railway lines or RSJs bent or welded at around a 60 degree angle — known as hairpins. In both cases, prepared sockets about 6 inches (15 cm) square were placed in the road, which, when not in use, were closed by covers, allowing traffic to pass normally.

Demolition chambers under a bridge over the Bridgwater and Taunton Canal — later filled with concrete and now appear larger than they originally were.

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 General Andrew McNaughton) was a horizontally bored pipe packed with explosives — once in place this could be used to instantly ruin a road or runway. Prepared demolitions had the advantage of being undetectable from the air — the enemy could not take any precautions against them, or plot a route of attack around them.

Crossing points in the defence network — bridges, tunnels and other weak spots — were called nodes or points of resistance. These were fortified with removable road blocks, barbed wire entanglements, and mines. These passive defences were overlooked by trench works, gun and mortar emplacements, and pillboxes. In places entire villages were fortified using barriers of scaffolding, sandbagged positions and loopholes in existing buildings.

Nodes were designated 'A', 'B' or 'C' depending upon how long they were expected to hold out. 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 usually had a garrison of regular troops.

The rate of construction was frenetic: by the end of September 1940, 18,000 pillboxes and countless other preparations had been completed.

Airfields and open areas

Open areas were considered vulnerable to invasion from the air: a landing by paratroops, glider-borne troops or even powered aircraft which could land and take off again. Open areas with a straight length of 500 yards (457 m) or more within five miles (8 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.

Securing an airstrip would be an important objective for the invader. Airfields, considered extremely vulnerable, were protected by trench works and pillboxes which face inwards towards the runway, rather than outwards. 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 difficult to defend large open areas without creating impediments to the movement of friendly aircraft. Solutions to this problem included the pop-up Picket Hamilton fort — a light pillbox that could be lowered to ground level when the airfield was in use. Another innovation was a mobile pillbox that could be driven out onto the airfield, this was known as the Bison and consisted of a lorry with a concrete armoured cabin and a small concrete pillbox on the flat bed.

Hardened field defences

Pillbox type FW3/22.

Main article: British hardened field defences of World War II

The field fortifications constructed throughout Britain included large numbers of hardened field defences: mostly in the form of pillboxes.

In May 1940, the Directorate of Fortifications and Works (FW3) was set up at the War Office. Its purpose was to provide a number of basic pillbox designs which could be constructed by soldiers and local labour at appropriate defensive locations. In the following June and July FW3 issued 6 basic designs for rifle and light machine gun pillboxes, designated Type 22 to Type 27. In addition, there were designs for gun emplacements suitable for either the Ordnance QF 2 pounder or the Hotchkiss 6pdr gun (designated Type 28) and a design for a hardened medium machine gun emplacement.

There were also designs for pillbox-like structures for various purposes including light anti-aircraft positions, observation posts and searchlight positions to illuminate the shoreline.

A small number of pillboxes had been constructed in the First World War and where possible these were integrated into the defence plans. Some pillboxes may predate the publication of the FW3 designs, but in any case some local commanders introduced modifications to the standard FW3 designs or introduced designs of their own. These non-standard design pillboxes may be produced in some numbers or completely ad hoc designs suited to local conditions. Other designs were produced as commercial ventures.

Other defensive measures

Other basic defensive measures included the removal of signposts and railway station signs making it more likely that an enemy would become confused. Pumps were removed from service stations near the coast and there were careful preparations for the destruction of those that were left lest they prove useful to the invader. Detailed plans were made for the destruction of anything that might prove useful to the invader such as port facilities, key roads and rolling stock.

In certain areas, non-essential citizens were evacuated. In the county of Kent, 40% of the population was relocated; in East Anglia, the figure was as high as 50%.

British poster of World War II.

Perhaps most importantly, the population was told exactly what was expected from them. In June 1940, the Ministry of Information published If the Invader Comes, what to do — and how to do it, it began:

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. 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].

The very first instruction given quite emphatically is that unless ordered to evacuate, 'THE ORDER IS "STAY PUT".' [Capitalization as in original]. 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 is British. Further: 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 — when ordered to do so — '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." [Capitalization as in original]

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.

In 1941, in towns and villages Invasion Committees were formed to ensure cooperation with the military and to plan for the worst should their communities be isolated or occupied. The members of such committees would typically include representatives of the local council, the Air Raid Precautions service, the Fire Service, the Police, the Women’s Voluntary Service and the Home Guard, as well as officers for medicine, sanitation and food. The detailed plans of these committees were kept in secret War Books although few of these valuable historical documents now 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. 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."

It is clear that more than merely passive resistance to the enemy was expected — or at least hoped for — from the civil population. Churchill considered the formation of a Home Guard Reserve, given only an armband and very basic training on the use of simple weapons such as Molotov cocktails. The reserve would only have been expected to report for duty in the event of an invasion. Later, Churchill wrote about 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]." He also later recorded how he intended to use the slogan "You can always take one with you."

Guns, petroleum and poison

In 1940, weapons were in critically short supply; there was a particular scarcity of anti-tank weapons, many of which had been left behind in France. Ironside had only 170 2-pounder anti-tank guns, but these were supplemented by 100 Hotchkiss 6-pounder guns dating from World War I, improvised into the anti-tank role by the provision of solid shot. By the end of July 1940, an additional 900 75 mm field guns had been received from the USA, — the British were desperate for any available means of stopping armoured vehicles.

One of the few resources not in short supply was petroleum oil; supplies originally intended for Europe were filling British storage facilities. Considerable effort and enthusiasm was put into making use of petroleum products as a weapon of war. The British Army had not had any flame throwers since the end of the First World War, but a significant number were hastily improvised from pressure greasing equipment acquired from automotive repair garages. Although limited in range, they were considered to be reasonably effective.

There were many ideas for using petroleum on a larger scale and although many of these proved fruitless a number of practical petroleum warfare weapons were developed.

A Mobile Flame Trap comprised surplus bulk storage tanks mounted on trucks, the contents of which could be hosed into a sunken road and ignited. A Static Flame Trap was prepared with perforated pipes running down the side of a road connected to a 600-imperial-gallon (2,730 L; 720 US gal) tank at an elevated position. Usually gravity sufficed but in a few cases a pump assisted in spraying the mixture of oil and petrol.

A flame fougasse comprised a 40 gallon light steel drum 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 to shoot a flame 10 feet (3 m) wide and 30 yards (30 m) long. They were usually deployed in batteries of four barrels and would be placed at a location such as a corner, steep incline or roadblock where vehicles would be obliged to slow down.

Variants of the flame fougasse included the demigasse, simply a barrel on its side and left in the open with an explosive charge buried just underneath; and the Hedge Hopper: a barrel stood on end with an explosive charge buried underneath a few inches deep and slightly off centre. On firing, the hedge hopper barrel was projected ten feet (3 m) into the air and over a hedge or wall behind which it had been hidden. 50,000 flame fougasse barrels were installed at 7,000 sites mostly in southern England and at a further 2,000 sites in Scotland.

Early experiments with floating petroleum on the sea and igniting it were not entirely successful: the fuel was difficult to ignite, large quantities of it were required to cover even modest areas of sea 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. Such installations consumed considerable resources and although this weapon was impressive, its network of pipes was very vulnerable to any pre-landing bombardment; General Brooke did not consider it to be effective. Initially ambitious plans were cut back to cover just a few miles of beaches.

It seems very likely that the British would have used poison gas against troops on beaches. General Brooke, in an annotation to his published war diaries, stated that he "...had every intention of using sprayed mustard gas on the beaches". 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.

Deception and disinformation

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, dummy pillboxes were constructed, and uniformed mannequins kept an unblinking vigil.

Volunteers were encouraged to make use of anything that would delay the enemy. 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. 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 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.

In 1938, a section funded by MI6 was created for the purpose of propaganda, headed by Sir Campbell Stuart. It was allocated premises at Electra House and was duly dubbed Department EH. On 25 September 1939 the unit was mobilised to Woburn Abbey 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). These SOE elements later 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 such false rumour stated that the British had a new kind of 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. Such rumours were evidently credible and rapidly spread. American broadcaster William Shirer recorded large numbers of burns victims in Berlin, though it is not entirely clear exactly what he personally saw it seems likely that his reports were influenced by the rumours. The interrogation of a captured Luftwaffe pilot revealed that the existence of such weapons was common knowledge, and documents found after the war showed that the German high command were completely deceived. The rumour seemed to take on a life of its own on both sides leading to a number of persistent stories of a thwarted German invasion, in spite of official British denials. 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.

Planned resistance

Main article: Auxiliary Units

The Auxiliary Units were a specially trained and highly secret organisation that, in the event of an invasion, would provide resistance behind enemy lines. Selected for their aptitude and for local knowledge, they were mostly recruited from the Home Guard — which also provided a cover for their existence. Organised into patrols of 4 to 8 men: each patrol was a self-contained cell, expected to be self-sufficient. Each patrol was provided with a concealed underground Operational Base, usually built in woodland and heavily camouflaged.

The Auxiliary Units were well-equipped and supplied with food for 14 days.

In addition, a network of civilian Special Duties personnel was recruited. They were to provide an intelligence gathering service, spying on and observing enemy formations and troop movements. Reports were to be collected from dead letter drops and relayed by radio operators of the Royal Signals from secret locations.

The threat recedes

After the evacuation of Dunkirk, people believed that the threatened invasion could come at almost any time. German preparations would require at least a few weeks, but all defensive precautions were made with an extreme sense of urgency. In the summer of 1940, an invasion attempt could occur any time, but some times were rather more likely than others: the phase of the moon, the tides and, most of all, the weather were considerations. The weather deteriorates significantly after September, but an October landing was not out of the question. 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.

The Battle of Britain had been won and on 12 October 1940, unknown to the British, Hitler rescheduled Sealion for the spring of 1941. By that spring, 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, the prime minister, Churchill, was able to say:

We are waiting for the long promised invasion. So are the fishes...

When, on 22 June 1941, Germany invaded the Soviet Union, it became 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. 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.

On 7 December 1941, a Japanese carrier fleet launched a surprise air attack on the American fleet at Pearl Harbor; by way of the German declaration of war this brought the USA into the war on Britain’s side and, given America's Germany first strategic policy, resources flooded into the UK. After nearly two years of waiting for the enemy, the danger of invasion was finally passed.

Would the preparations have been effective?

General Brooke frequently confided his concerns to his private diary. When published, he included additional annotations written many years later:

...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. [Italics in original]

The question of whether the defences would have been effective in the event of an invasion is a vexed one. In the summer of 1940, the preparations relied heavily upon field fortifications. The experiences of the First World War made it clear that assaulting prepared defences with infantry was deadly difficult, but similar preparations in Belgium had been easily overrun by the well-equipped German Panzer divisions in the early weeks of 1940 and with so many armaments left behind 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 about 2,000 converted barges and other vessels had been hurriedly made available and their fitness for the purpose 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.

The later experiences of American forces on Omaha Beach on D-day and taking on Japanese defenders on Pacific islands clearly 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.

In the event of an invasion, the Royal Navy would have sailed to the landing places — possibly taking several days to get there. It is now known that the Germans planned to land on the southern coast of England, one reason for choosing this site was that the narrow seas of the English channel could be blocked off with mines, U-boats and torpedo boats. While German naval forces and the Luftwaffe could doubtless have extracted a high price from the 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 — 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 somewhat more equal terms than might otherwise have been the case 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 counter attack.

Scholarly consideration of the likely outcome of a German invasion, including wargames held at Royal Military Academy Sandhurst in 1974, generally agree that while German forces would have been able to land and gain a significant beachhead, the intervention of the British 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 ultimately have been defeated.

Having failed to gain even local air superiority in the Battle of Britain, Operation Sealion was postponed indefinitely. However, it seems clear that Hitler and his generals were well aware of the problems of mounting an invasion. Hitler was not ideologically committed to a long war with Britain and many commentators have suggested that German invasion plans were a feint never intended to be put into action.

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 at will anywhere in southern England and with the prospect of an invasion, the British government would have come under enormous 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.

See also

• Eastbourne Redoubt Home of the Combined Service Museum
• Dymchurch Redoubt

References

General references

• Alanbrooke, Field Marshal Lord (2001). War Diaries 1939–1945. Phoenix Press. ISBN 1-84212-526-5.
• Banks, Sir Donald (1946). Flame Over Britain. Sampson Low, Marston and Co.
• Cameron, A Bryce (2000). Under Sand, Ice & Sea. Trafford Publishing. ISBN 1-55212-319-7.
• Churchill, Winston (2005). Their Finest Hour. The Second World War, Volume II. Penguin. ISBN 0-141-44173-9. {{cite book}}: Unknown parameter |origdate= ignored (|orig-date= suggested) (help)
• Cox, Richard (1974). Operation Sea Lion. Thornton Cox. ISBN 0-902726-17-X.
• Cruickshank, Dan (2001). Invasion — Defending Britain from Attack. Boxtree. ISBN 0-7522-2029-2.
• Evans, Martin Marix (2004). Invasion! Operation Sealion 1940. Longman. ISBN 0-582-77294-X.
• Fleming, Peter (1957). Invasion 1940. Rupert Hart-Davis.
• Foot, William (2006). Beaches, fields, streets, and hills ... the anti-invasion landscapes of England, 1940. Council for British Archaeology. ISBN 1-902771-53-2.
• Gillies, Midge (2006). Waiting for Hitler — Voices from Britain on the Brink of Invasion. Hodder & Stoughton. ISBN 0-340-83798-5.
• Hayward, James (2001). The Bodies On The Beach — Sealion, Shingle Street and the Burning Sea Myth of 1940. CD41 Publishing. ISBN 0-9540549-0-3.
• James, Brian (2006). "Pie in the Sky". History Today. {{cite journal}}: Unknown parameter |month= ignored (help); Unknown parameter |quotes= ignored (help)
• Liddell Hart, Basil (1958). The German Generals Talk. Berkley Publishing. {{cite book}}: Unknown parameter |origdate= ignored (|orig-date= suggested) (help)
• Lowry, Bernard (2004). British Home Defences 1940–45. Osprey Publishing. ISBN 1-84176-767-0.
• Mace, Martin (2001). Vehicles of the Home Guard. Historic Military Press. ISBN 1-901313-08-5. {{cite book}}: Unknown parameter |month= ignored (help)
• MacKenzie, S. P. (1995). The Home Guard — A Military and Political History. Oxford University Press. ISBN 0-19-820577-5.
• Osborne, Mike (2004). Defending Britain ... twentieth century military structures in the landscape. Tempus Publishing. ISBN 0-7524-3134-X.
• Ruddy, Austin (2003). British Anti-Invasion Defences 1940–1945. Historic Military Press. ISBN 1-901313-20-4.
• Ward, Arthur (1997). Resisting the Nazi Invader. Constable and Co. ISBN 0-09-476750-5.
• White, John Baker (1955). The Big Lie. Evans Brothers.
• Wills, Henry (1985). Pillboxes: A Study of UK Defences. Leo Cooper. ISBN 0-436-57360-1.

Official documents

• Consolidated Instructions to Invasion Committees in England and Wales (July 1942) HM Government.
• Barrel Flame Traps, Flame Warfare: Military Training Pamphlet No. 53. Part 1 (July 1942) The War Office.

Collections

• "The National Archives". repository of UK government records. Retrieved 2007-02-19.
• "WW2 People's War". BBC. Retrieved 2007-02-19. - 'WW2 People's War is an online archive of wartime memories contributed by members of the public and gathered by the BBC. The archive can be found at bbc.co.uk/ww2peopleswar'

Further reading

• William Foot - The Battlefields That Nearly Were. Defended England 1940 (Stroud:Tempus Publishing 2006) ISBN 9780752438498
• Mike Osborne - 20th Century Defences in Britain (Stroud:Tempus Publishing 2003) ISBN 0-9540378-1-2
• C Bird -Silent Sentinels - A study of the fixed defences constructed in Norfolk during WWI and WWII (Dereham: The Larks Press 1999) ISBN 0-948400-81-1
• Stewart Ross - World War II Britain. History from Buildings (London:Franklin Watts 2006) ISBN 0-7496-6468-1

External links

• The German Threat to Britain in World War Two. By Dan Cruickshank. BBC website.
• The Real Dad's Army - TV Documentary.
• Advanced Wargames
• Churchill's mysterious map.
• Pillboxesuk.co.uk.
• Defence of Britain database.