British anti-invasion preparations of the Second World War

Detail from a pillbox embrasure.

In May 1940, during World War II, German and Italian forces invaded France and the Low Countries, the ensuing Battle of France resulted in the retreat of the Allied forces, the evacuation of the British Expeditionary Force and allies from the beaches of Dunkirk, and, finally, the capitulation of France.

At this time, the threat of invasion, which had recurred from time to time in the preceding centuries, again became a serious possibility. The British Government responded with a massive programme of military and civilian mobilisation. The rapid construction of field fortifications transformed much of Britain, especially southern England, into a prepared battlefield. Woefully 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.

Early beginnings

On September 1 1939, Germany invaded Poland; two days later, Britain and France declared war on Germany thereby joining the Second World War. Within three weeks, the Red Army of the Soviet Union invaded the eastern regions of Poland in fulfilment of a secret with Nazi Germany. A British Expeditionary Force (BEF) was sent to the Franco-Belgian border, but Britain and France could not take any direct action in support of the Poles in the time available. By 1 October, Poland was completely overrun. There was little fighting and over the many quiet months that followed; in a period known as the Phoney War, the British soldiers trained for war and constructed and manned defences.

On April 9 1940, Germany invaded Denmark and Norway, after some fierce fighting both countries fell to German occupation. 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 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 about 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 British defences: 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 went badly for allies in France, it became evident that some thought must be given to the possibility of having to resist an attempted invasion by German forces.

British armed forces

The British Army

British prisoners at Dunkerque, 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 without even their rifles.

In June 1940, the British army had 22 divisions of infantry and one of armour. The infantry divisions were, on average, at just half strength and 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.

The 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 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. One of the first of these weapons was the Sticky bomb, 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: none-the-less, more than two million were made. Other early examples included the No 76 Special Incendiary Grenade (a glass bottle filled with highly inflammable material), the No. 73 Grenade (an anti-tank grenade resembling a Thermos flask). A measure of mobility was provided by bicycles, private vehicles and even horses.

Later in the war, 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). And some units were even equipped with armoured cars.

The Royal Air Force

Main article: Battle of Britain

In the summer of 1940, the principle occupation 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, any airfield that was in danger of being captured would be made inoperable and there were plans to remove all portable equipment from vulnerable radar bases and destroy completely 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. A much-reduced air force would have been obliged to operate from airfields well away from the south east of England. To fly in the presence of an enemy that enjoys air superiority is very dangerous although the RAF would have enjoyed certain advantages such as being able to operate largely over friendly territory. Also, until the Germans were able to operate from airfields in England, Luftwaffe pilots would still have to fly a significant distance.

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

The Royal Navy

The British Home Fleet was a force that dwarfed anything the Kriegsmarine could put to sea. On 1 July there was one cruiser and 23 destroyers committed to escort duties in the Western Approaches. Also committed to escort duties were 10 destroyers 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, an additional cruiser and 2 destroyers on the Tyne 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 destroyers were transferred from escort duties to defence of the homeland, and more were on the way.

Field fortifications

The British engaged upon a massive programme of field fortification.

On the 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 so-called 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. GHQ Line 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 protected England's south-west peninsular and the port city of Bristol; 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 this is entirely unfair as he always understood the limits of the stop lines and never expected them to hold out indefinitely.

However, some officers were said to be becoming obsessed with concrete and a new focus was required. On 19 July 1940, Ironside was replaced by General Brooke (later known as Lord Alanbrooke). His 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 were established each having all-round defence. Many of these anti-tank islands were established along the existing 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.

Any invasion requires 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, in the main, 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.

Concertina wire.

Beaches were blocked with enganglements 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 demark 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.

Where a barrier to tanks was required, obstacle Z1 (also known as Admiralty Scaffolding) 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. Z1 was deployed along hundreds of miles of vulnerable beaches.

An even more robust barrier to tanks was provided by long lines of anti-tanks 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.

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

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 frequently 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 obstacles of reinforced concrete that were either cubic or cylindrical. The cubes generally came in two sizes: 5 feet (1.5 m) or 3.5 feet (1 m). 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 range in size somewhat, but are 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 sport 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 wood posts would suffice.

Removable roadblock at a bridge on the Basingstoke Canal.

Roads and railways offered the enemy fast routes to their objectives — tanks could move easily along railways. Many roadblocks were formed by General Ironside that were semi-permanent. In many cases, General Brooke had these removed altogether as experience had shown they could be as much of an impediment to friends as foes. Brooke favoured removable blocks.

The simplest of the removable roadblocks and railblocks were massive concrete posts with holes and/or slots to accept horizontal railway lines or rolled steel joists (RSJs). 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. These removable roadblocks could be opened or closed within a matter of minutes.

Sockets for hedgehog removable roadblock on 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, this was known as hedgehog. The second comprised railway lines or RSJs bent or welded at about a 60 degree angle — known as hairpins. In both cases, pre-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.

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 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 so that an enemy would not take any special precautions or know in advance to avoid them, thus an enemy could be taken by surprise.

Mines were also used, but much more sparingly that at the coast.

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

Airfields and other 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 obstacles such as concrete or wooden posts, sections of concrete pipe or even old cars.

Airfields themselves could be vulnerable: these were protected by trench works and pillboxes which face not outwards as might be expected, but inwards towards the runway. Many of these fortifications were specified by the Air Ministry and the designs are unique to airfields.

Hardened field defences

Pillbox type FW3/22.

Light Anti-aircraft Position.

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 of 1940, the directorate of Fortifications and Works (FW3) was setup at the War Office under the direction of Major-General G. B. O. Taylor. 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, 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. In addition, the Air Ministry provided designs of fortifications intended to protect airfields from troops landing or parachuting. These would not be expected to face heavy weapons so that the degree of protection was less and there was more emphasis on all-round visibility and sweeping fields of fire. Many of these were later reinforced.

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

British poster of World War II.

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

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".' [Capitalisation 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 and 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." [Capitalisation as in original].

Further similar leaflets followed, with, for example, more specific instructions for farmers. Later, in 1941 there was a leaflet written by the Prime Minister, Winston Churchill.

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 even 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 very few of these valuable historical documents now remain. Detailed inventories of anything useful were kept: vehicles, animals, basic tools etc., 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.

Guns, gasoline and poison

In 1940, weapons were in critically short supply. There was a particular shortage of anti-tank weapons, many of which had been left behind in France. The 2 pounder anti-tank gun was in short supply, Ironside had only 170 available, it was supplemented by 100 Hotchkiss 6pdr guns dating from WWI improvised into the anti-tank role by the provision of solid shot. By July 1940 an additional 100 75 mm field guns had been received from the USA, welcome as these undoubtedly were, 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 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 the ideas proved fruitless a number of practical petroleum warfare weapons were developed. Mobile land barrages comprised surplus bulk storage tanks mounted on trucks, the contents of which could be drained 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-gallon 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 was a 40-gallon drum dug into the roadside and camouflaged. It would be placed at a location such as a corner, steep incline or roadblock where vehicles would be obliged to slow down. Guncotton provided the propellant charge which, when triggered, caused the weapon to shoot a flame 10 feet (3 m) wide and 30 yards (30 m) long. They were usually deployed in batteries of four barrels. The Demigasse was similar to the Flame Fougasse, but was placed in the open. 50,000 flame fougasse barrels were installed at 7,000 sites mostly in southern England and at a further 2,000 sites in Scotland. The Hedge Hopper was a barrel of petroleum mixture with an explosive charge placed underneath slightly off centre. On firing, the barrel would be projected ten feet (3 m) into the air and over a hedge or wall behind which it had been hidden. Early experiments with floating petroleum on the sea and igniting it were not entirely successful: the fuel was difficult to ignite, large quantifies 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 ambitions plans were cut back to cover just a few miles of beaches.

It seems very likely that the British planned to use 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 somehow 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, it was allocated premises at Electra House and was duly dubbed Department EH. On the very day that Germany invaded Poland, the unit was mobilised to Woburn Abbey where it joined a subversion team from MI6 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 spread false rumours. 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. 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 taken in. 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 the 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 specially trained and highly secret units 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 cells 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, the threatened invasion could come at almost any time. To be sure, the German preparations would require at least a few weeks, but all defensive precautions were made with an extreme sense of urgency — during the summer of 1940, the enemy could be expected at any time. Some times were rather more likely than others: the phase of the moon, the tides and, most of all, the weather were all considerations. The weather deteriorates significantly after September, but an October landing was not out of the question. On the 3rd of 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 darkly: We are waiting for the long promised invasion. So are the fishes...

When on June 22, 1941, the Germans made war on 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 December 7, 1941 a Japanese carrier fleet launched a surprise air attack on the American fleet at Pearl Harbor; this brought the USA into the war on Britain’s side and, especially 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 past.

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. On the one hand, 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 armoured divisions. 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 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 extract a terrible price from assaulting forces.

In the event of an invasion, the 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 bridgehead, the intervention of the British navy would be 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.

Of course, 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.

References

• Alanbrooke, Field Marshal Lord. War Diaries 1939-1945. Phoenix Press, 2001 ISBN 1842125265.
• Banks, Sir Donald. Flame Over Britain. Sampson Low, Marston and Co, 1946.
• Cameron, A Bryce. Under Sand, Ice & Sea. Trafford Publishing, 2000 ISBN 1552123197.
• Cox, Richard. Operation Sea Lion. Thornton Cox, 1974 ISBN 090272617X.
• Cruickshank, Dan. Invasion — Defending Britain from Attack. Boxtree, 2001 ISBN 0752220292.
• Evans, Martin Marix. Invasion! Operation Sealion 1940. Pearson Education Limited, 2004 ISBN 058277294.
• Foot, William. Beaches, fields, streets, and hills ... the anti-invasion landscapes of England, 1940. Council for British Archaeology, 2006 ISBN 1902771532.
• Hayward, James. The Bodies On The Beach — Sealion, Shingle Street and the Burning Sea Myth of 1940. CD41 Publishing, 2001 ISBN 0954054903.
• Lowry, Bernard. British Home Defences 1940–45. Osprey Publishing, 2004 ISBN 1841767670.
• MacKenzie, S. P. The Home Guard — A Military and Political History. Oxford University Press, 1995 ISBN 0198205775.
• Osborne, Mike. Defending Britain ... twentieth century military structures in the landscape Tempus Publishing, 2004 ISBN 075243134X
• Ruddy, Austin. British Anti-Invasion Defences 1940–1945. Historic Military Press. 2003 ISBN 1901313204.
• White, John Baker. The Big Lie.Evans Brothers, London 1955.
• Willis, Henry. Pillboxes: A Study of UK Defences. Leo Cooper. 1985 ISBN 0436573601.
• 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 http://bbc.co.uk/ww2peopleswar.
• The Stanton Ironworks Co. Stanton at War 1939-45. The story of the part played by Stanton Ironworks with reference to making of the concrete sections for a Ruck Machine gun post/Pillbox.

Further reading

• William Foot - Beaches, fields, streets, and hills ... the anti-invasion landscapes of England, 1940 (Council for British Archaeology, 2006) ISBN 1902771532
• Mike Osborne - Defending Britain ... twentieth century military structures in the landscape (2004) ISBN 075243134X
• Austin J Ruddy - British Anti-Invasion Defences 1940–1945 (2003 Historic Military Press) ISBN 1901313204
• Mike Osborne - 20th Century Defences in Britain (2003) ISBN 0954037812
• C Bird -Silent Sentinels - A study of the fixed defences constructed in Norfolk during WWI and WWII (1999) ISBN 0948400811
• Ian Sanders - Pillboxes - Images of an Unfought Battle (2005 Lulu Press) ISBN 1411626516

External links

General

• The German Threat to Britain in World War Two. By Dan Cruickshank. BBC website.
• The Real Dad's Army - TV Documentary.
• Advanced Wargames
• Pillboxes for bats.
• Pillboxes on BBC Inside Out website.
• English Heritage: Understanding & Recording Military Sites.
• Churchill's mysterious map.
• Building Pillboxes: A Personal Story by E. S. Hardie.
• Pillboxesuk.co.uk.

National

• Defence of Britain database.
• Pillbox study group.
• Pillbox Study Group Details of many specific sites throughout Britain.
• Pillboxes UK Details of many specify sites throughout Britain.

Regional

• Cumbria: Defence of Cumbria in the 20th Century.
• Cumbria: Defence of the port of Workington.
• Devon: Eastern Devon around Seaton and Axmouth.
• Dorset: Isle of Purbeck, Abbotsbury.
• Hampshire: Defences at Breamore Mill, Downton, Hamphire.
• Hampshire: Defending Chequers Bridge, Crookham Village, Hampshire by Colin Alexander.
• Hertfordshire: Fortress Hertfordshire.
• Kent: Pillboxes of WW2 Dover and Western Heights.
• Kent: Dover and Western Heights.
• Norfolk: WW2 Coastal Defences Salthouse, Kelling & Weybourne North Norfolk
• Norfolk: 20th Century Defensive Structures...
• Northumberland: 20th Century Defensive Structures...
• Orkney: 20th Century Defensive Structures...
• Somerset: Somerset pillboxes.
• Surrey: Pillboxes in Surrey.
• Sussex: Newhaven.
• West Sussex: 1940 in Findon Stories and photographs of a fortified village on Britain's southern coast.
• Yorkshire: The Defences of a Coastal Inlet, Sand-le-Mere, East Yorkshire by Austin J Ruddy.