British anti-invasion preparations of the Second World War

Invasion of Britain (prospective)
Part of World War II
A dated embrasure from the hardened field defences constructed in preparation for an expected German invasion.
Date 1940–41 Location United Kingdom Result Invasion never took place

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 for centuries been at most a theoretical contingency, 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, now known to us as Operation Sealion, was never put into effect.

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

As things went badly for the British Expeditionary Force in France, it became evident that some thought must be given to the possibility of having to resist an attempted invasion by German forces.

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.

On May 26 1940, Operation Dynamo (the evacuation of the British and allied forces from Dunkirk) began. Most of the personnel were brought back to Britain, but many of the army's vehicles, tanks, guns, ammunition and heavy equipment were left behind in France.

There were plenty of personnel for the defence of the country, but equipment was in critically short supply.

Lines and islands

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 entirely static and focused on the coastline 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 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, especially at towns and villages where there was a Home Guard to provide personnel. However, the stop lines were not entirely abandoned.

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. It was always recognised that it was not possible to hold off a determined attack forever. 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. Pre-existing barriers were supplemented with anti-tank obstacles such as ditches, massive concrete blocks (generally cubic or cylindrical) and pyramid shaped concrete blocks popularly known as dragons teeth.

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 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.

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.

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.

Weapons

British Home Guard Improvised Weapons

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.

The British defence relied heavily on improvisation and ingenuity. At first, the Home Guard was armed with whatever was available: guns in private ownership, a knife or bayonet on a pole and Molotov cocktail. Soon, the Home Guard arsenal included weapons that the regular Army no longer required and weapons that could be produced cheaply without consuming materials that were needed to produce armaments for the regular units. These included the Blacker Bombard anti-tank weapon, the Sticky bomb, the Northover Projector (a black powder powered mortar), 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), and the Smith Gun (a small artillery gun that could be towed by a private motorcar).

Minefields were laid with both anti-tank and anti-personnel mines. Bridges were prepared for demolition at short notice, often by placing explosives into prepared detonation chambers. The Canadian Pipe Mine (also called a McNaughton Tube) was a bored pipe packed with explosives — once in place this could be used to instantly ruin a road or runway. A Depth Charge Crater was a site prepared with buried explosives that could be detonated to instantly form a deep crater as an anti-tank obstacle.

A Barrel Flame Trap was a site prepared with a barrel of petrol (gasoline) to be discharged across a road and then ignited.

A Flame Fougasse was a barrel filled with a mixture of petrol, oil and rubber — which in time becomes sticky — to be fired by an explosive charge. Usually dug into roadside banks.

At the coast, Petroleum Warfare Sites were prepared where a petrol based mixture could be piped onto the shore, and even into the water, and ignited. Although this weapon was impressive, its network of pipes was very vulnerable to any pre-landing bombardment and was easily disrupted by sea waves. General Brooke did not consider it to be effective.

General Brooke remarked in his published war diaries that he "...had every intention of using sprayed mustard gas on the beaches".

Barriers and obstacles

Concertina wire.

Barbed wire

Barbed wire usually took the form of either wire entanglements in the form of three coils of concertina wire fixed by metal posts — called Triple Danert Wire Fencing — or a simple fence of straight wires supported on waist high posts.

Anti-tank Scaffold Fencing

Obstacle Z1 was a fence made of scaffolding poles and was deployed at low water along vulnerable beaches. Essentially, it was a fence of scaffolding tubes 9 feet (3 m) high. It was intended to be an obstacle to tanks and was placed at low water so that they could not get a good run at it.

Similar obstacles of scaffolding were constructed to block the gaps between buildings in fortified buildings.

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

Anti-tank Ditch

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. Because agricultural land was valuable, the ditches were quickly filled in after the war.

Anti-tank cubes.

Anti-tank cylinder.

Anti-tank Obstacles

The most common anti-tank obstacles were simple cubes or cylinders of reinforced concrete.

The cubes generally came in two sizes: 5 feet (1.5 m) or 3.5 feet (1 m).

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.

Anti-tank walls were also constructed — essentially continuously abutted cubes.

There was also a tetrahedral or caltrop-shaped obstacle, although it seems these were rare.

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

Removable roadblock at a bridge on the Basingstoke Canal.

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

Road and rail blocks

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.

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 placed in the road. When not in use, the sockets were closed by covers.

Demolition charges

Bridges and other key points were prepared for demolition at short notice by preparing chambers filled with explosives.

Hardened field defences

Precast pillbox embrasure with shutter.

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 further 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.

Local commanders introduced their own designs. For example, unique to the north east of England were the lozenge and eared pillbox designs. Furthermore, some pillboxes were completely ad hoc designs suited to local conditions.

The basic designs were adapted to local circumstances and available building materials such that, outwardly, two pillboxes of the same basic design could look quite different. The height of a pillbox could vary significantly according to local needs: some were half buried so that the embrasures might be as low as ground level, others were raised up to give a better view; those built into hillsides might lack embrasures on some walls; the entrance could be moved and its size varied as might be convenient and there may be additional walls to protect the entrance, a freestanding blast wall or a steel door.

Embrasures were generally precast and factory produced to standard designs, but as these were in short supply some embrasures were improvised from brick or concrete paving. Embrasures were frequently fitted with a steel or concrete-asbestos shutter. From March 1941, some pillbox embrasures were fitted with a Turnbull mount, this was a metal frame that supported a medium machine gun.

Appearance also varied due to the building materials used, although all are formed from reinforced concrete. Where brick was used as a shuttering, the bricks essentially formed a mould into which concrete was poured, the bricks being left in place. Otherwise, the pillbox was formed using shuttering of wood (usually planks, but sometimes plywood) and/or corrugated iron. Wood shuttering was removed, whereas corrugated iron was sometimes left in place.

The degree of protection offered by a pillbox varied considerably. The thickness of the walls and roof varied from just 12 inches (30 cm) to 3.5 feet (1 metre) or more. Generally speaking, the thinner-walled pillboxes were intended to be bullet proof whereas the thick-walled pillboxes were intended to be shell proof.

Construction often took advantage of whatever materials were available locally. For example, at the coast, beach sand and pebbles would be used. Use of local materials had the added advantage of aiding camouflage. The reinforced concrete used in construction was generally conventional making use of thin steel rebars with floor, walls and roof all mutually bonded. However, at least one case is known where scrap metal had been used: the concrete was reinforced with parts of an old bed.

Internally, pillboxes are generally cramped and spartan. Some internal concrete shelves and tables were provided to support weapons and some were whitewashed inside. At night, blue light was favoured. Only the Type 28s provided a little space.

FW3 pillbox types

The approximate numbers of extant pillboxes of each type are given based on data from the Defence of Britain database.

Pillbox type FW3/22.

Type 22

The type 22 pillbox is a regular hexagon in plan with an embrasure in five of the sides and an entrance in the other. The embrasures are suitable for rifles or light machine guns. Some have a low entrance that allows an extra embrasure above. Each wall is about 6 feet (1.8 m) long and it was generally built to the bullet proof standard of 12 inches (30 cm) thick, although 'tank-gun proof' versions with walls around 1 m thick were also built (e.g. the granite and concrete examples on the Cowie Line in Kincardineshire). Internally there is a Y- or T- shaped anti-ricochet wall (the top of the Y/T nearest the entrance), the internal wall also helps support the roof.

The type 22 is the second most common pillbox type with just over 1000 recorded as being extant. It is easily confused with the common type 24 which is an irregular hexagon and the less common octagonal.

Pillbox type FW3/23.

Type 23

The type 23 pillbox is rectangular in plan — essentially two squares, one of which is roofed and the other open — with three embrasures, one in each of the available sides of the covered section. The embrasures are suitable for rifles or light machine guns. The open section was for a light anti-aircraft defence: a Bren or Lewis gun on a mounting. Usually, there is no ground level entrance, to get in one had to climb over the wall into the open section and then pass though a door to the covered section. The walls were 8 feet (2.4 m) wide by 16 feet (4.8 m) long and usually built to a bullet proof standard of 12 inches (30 cm) thick.

The type 23 is uncommon, just over 100 are recorded as being extant.

Pillbox type FW3/24.

Type 24

The type 24 pillbox is an irregular hexagon in plan. The rear wall is the longest at about 14 feet (4.3 m), this has the entrance with an embrasure on either side. The other walls vary from 7-8 feet (2.2-2.5 m) each having a single embrasure. The embrasures are suitable for rifles or light machine guns. Internally there is a Y shaped anti-ricochet wall (the top of the Y nearest the entrance), the internal wall also helps support the roof. The type 24 was always built to at least bulletproof standard of 12 inches (30 cm) thick, but often was thicker.

A thick walled variant was introduced to a shellproof standard; it was larger externally and had walls 36-50 inches (91-127cms), thick. (This thick-walled variant is, confusingly, sometimes called a Type 29 by pillbox researchers, but this is not an official designation and should be avoided.)

The type 24 is easily the most common type with more than 1500 recorded as being extant.

Pillbox type FW3/25.

Type 25

The type 25 pillbox is the only FW3 design that is circular with a diameter of 8 feet (2.4 m). The walls were just 12 inches (30 cm) thick with no internal walls. There were three embrasures suitable for rifles or light machine guns and a small entrance like a low window. This design was made from reinforced concrete shuttered by corrugated iron; this gave the design the popular name Armco after the manufacturer of corrugated iron of that name.

The type 25 is rare, about 40 are recorded as extant.

Type 26

The type 26 is a simple square in plan, each wall being 10 feet (3 m) long. There is a door in one side and embrasures in each of the remaining three walls with, possibly, an addition embrasure next to the door. There are no internal walls. Occasionally, there are two embrasures in one of the walls. The embrasures are suitable for rifles or light machine guns. Walls are normally constructed to bullet proof standard at about 18 inches (45 cm) thick.

Pillbox type FW3/26, prefabricated construction.

The type 26 also had an important prefabricated variant, the shuttering — both inside and out — was provided by precast concrete slabs slotted into reinforced concrete posts.

The type 26 is uncommon, about 150 are recorded as extant.

Type 27

The type 27 is the most varied of the FW3 designs, it may be an octagonal or hexagonal in plan with walls between 9 feet 9 inches (3 m) and 11 feet 7 inches (3.5 m). The outer walls being 36 inches (90 cm) thick and having an embrasures are suitable for rifles or light machine guns on each facet. Its defining characteristic is a central well open to the sky that could be used as a light anti-aircraft position.

Type 27 is uncommon, about 80 are recorded as extant.

Pillbox type FW3/28A.

Pillbox type FW3/28A twin.

Type 28

The type 28 is the largest of the FW3 designs and the only one with a specific anti-tank capability. It is almost square in plan with the forward facing corners chamfered. The walls are each about 20 feet by 19 feet (6.1 m by 5.8 m) long constructed to shell-proof specification at about 42 inches (110 cm) thick. There is a very large forward embrasure. It was designed to take a 2 pounder anti-tank gun or a Hotchkiss 6pdr gun. The gun shield of the artillery piece would largely fill the aperture. There are usually embrasures suitable for rifles or light machine guns in each of the two side walls.

Superficially, the type 28 resembles the smaller Vickers MMG emplacement, but the aperture is much larger and there is a very large rear entrance designed for ease of wheeling the gun in and out.

The type 28A is an important and common variant. It is wider than the type 28 to allow for a side area for an infantry chamber giving a forward facing embrasure suitable for a rifle or light machine gun. This resolved the problem of the type 28 being vulnerable to a head-on infantry attack.

A further, rare, variant is the type 28A twin which has two main gun embrasures on adjacent walls giving two possible firing positions for the one main gun and together with two adjacent infantry sections.

The traverse of the gun was limited to about 60°. Generally, these pillboxes were positioned to fire along fixed lines, such as enfilading fire across an anti-tank ditch or at a bridge and in such positions the limited traverse of the gun creates no real disadvantage; whereas, the small size of the embrasure provides greater protection for the gun and its crew.

The type 28 and its variants are fairly common, there are some 350 or so recorded as extant.

Vickers MMG emplacement.

Vickers MMG emplacement

The Vickers machine gun pillbox is essentially square in plan with the forward facing corners chamfered. The walls are 14 feet (4 m) long and there is generally a freestanding blast wall covering the entrance on either the left or right side. The walls were constructed to shellproof standard of 36 inches (90 cm). There are no internal walls. There is a large embrasure and inside is a concrete, trapezoidal table on which to mount the weapon's tripod. The other walls would each have an embrasure suitable for a rifle or light machine gun.

These emplacements are only to be found on the Taunton Stop Line and on GHQ Line around Aldershot. They are frequently sited in pairs and were often dug-in with overhead earth cover.

Vickers MMG emplacements are uncommon, just over 75 are recorded as extant.

Other hardened defences

Field gun emplacement

Field gun emplacements

There were a wide variety of field gun emplacements, most resembled larger version of the Type 28 pillbox.

Lozenge pillbox

Lozenge pillbox

The lozenge pillbox is found only in the North East of England. Lozenge pillboxes are an irregular hexagon in plan with the front and rear walls significantly longer than the others, this allows space for four forward-facing embrasures. The rear wall has two embrasures and an entrance. The four short walls each have a single embrasure. Internally, an anti-ricochet wall runs longitudinally. It was designed for infantry armed with rifles and/or light machine guns.

Eared pillbox

Eared pillbox

The eared pillbox is, like the lozenge pillbox, found only in the North East of England and has an irregular hexagon plan. There are two large embrasures intended for medium machine guns. There is a bulge at the base of the wall below the embrasures that is thought to have accommodated the cooling system for the machine gun. Internally, there is a short anti-ricochet wall.

The two embrasures are at 90° to each other giving an arc of fire of about 180° with no way to direct fire behind the pillbox. This design is frequently found on or near beaches — ideal for providing enfilading fire. There are two entrances with openings in the same direction as the embrasures.

Lincolnshire three-bay pillbox.

Lincolnshire three-bay

Found only in Lincolnshire, this type has become known as a Lincolnshire three-bay pillbox. It is essentially a modification of the FW3 type 23 having an open light anti-aircraft position in the centre and fully enclosed bays at either end.

Coastal searchlight.

Coastal Searchlight

Dover quad pillbox.

Dover Quad

The Dover Quad pillbox is a 13 ft (4 m) square pillbox with wide embrasures and an overhanging roof slab. This design is only found in the Dover area of England.

Section post interior.

Section post

Section posts are essentially hardened trechworks. Constructed to bullet proof standard, they are long and have a large number of embrasures. Shelves of wood or concrete are fitted below the embrasures in the principle direction.

Somerset Defence Post

The defence post is only found in Somerset, it is about 8 feet (2.4 m) square with walls about 15 inches (38cm) thick and have wide slits extending the full width of three faces. There is a porch covering the entrance. Some have an open section on top reached by rungs and a ladder.

Octagonal pillbox. Note details such as the sloped roof edge and sculpted roof top.

Octagonal pillbox

Norcon Pillbox.

Norcon pillbox

The Norcon was a small circular pillbox named after the company that manufactured it as a private commercial venture. It was made from a concrete pipe 6 feet (1.8 m) diameter and 4 feet (1.2 m) high, the walls were 4 inches (10 cm) of non-reinforced concrete with several cut loopholes. Described as being possibly the most dangerous, cheap and nasty of all the pillbox designs. Being quick to manufacture was its biggest asset, it was possible to turn out about 20 a day the concrete being cured in about 24 hours but few were actually built. A roof made of timber and corrugated iron, and earth; extra protection was provided by the use of sandbags.

Ruck machine gun post.

Ruck machine gun post/pillbox

Designed by James Ruck, constructed from Stanton air raid shelter sections, the segments were made at the Stanton Ironworks Ilkeston Derbyshire in the Concrete Plant which converted from production of concrete lighting columns during the war the segments were 20 inches (50 cm) wide and 2 inches (5 cm) thick, a pair of them formed an arch 7 feet (2.1 m) high and transverse struts were provided to ensure rigidity. These fitted into longitudinal bearers, which were grooved to receive the foot of each segment. Each pair of segments were bolted together at the apex of the arch and each segment was also bolted to it neighbour, the joints being sealed with bituminous compound. The convenient handling of theses segments enabled them to be transported with ease. Partly buried in the ground and covered with turf and sandbags, with a suitably screened entrance, this bolted arch construction afforded safe protection against blast and splinters.

Pickett-Hamilton Fort, Imperial War Museum, Duxford

Pickett-Hamilton Fort

The need to defend airfields presented special problems. Airfields were large open areas where any above-ground structure would present a hazard to aircraft. One solution was the Pickett-Hamilton Fort, this was designed to be lowered to ground level while aircraft were operating, but to be raised when necessary by means of a hydraulic mechanism. The fort was manned by a crew of two with light machine guns. Access was provided by means of a hatch in the roof. The forts were prone to flooding and they were not sufficiently strong to bear the weight of the heavy aircraft developed during the war.

Alan Williams Turret, Imperial War Museum, Duxford

Alan Williams Turret

Pillbox formed by a revolving metal turret set above a steel and brick-lined pit.

Tett Turret

The Tett Turret was produced commercially by the Burbridge building company of Surrey. It was a two-man pillbox with a revolving concrete turret mounted on a ball race set above a cylindrical concrete pit formed by a standard section of concrete pipe 4 feet (1.2 m) in diameter. The top was open and vulnerable to a well thrown grenade, it provided the only means of egress which would have been very dangerous under fire.

Spigot mortar emplacement (reconstructed around extant pedestal).

Spigot mortar emplacement

A spigot mortar emplacement was unroofed, sometimes constructed of brick or concrete, but may be a simple reveted earthwork. Its defining characteristic is a central concrete pedestal with a stainless steel peg (rust free even after more than 60 years). The pedestal was for a type of spigot mortar called the Blacker Bombard — effective against both tanks at a range of about 100 yards (90 m) and personnel at a range of about 500 yards (460 m).

An embrasured wall.

Embrasured walls and buildings

Existing walls and building provided a ready-made alternative to a pillbox. Whatever may be lacking in protection was made up for by speed and convenience.

Camouflage

Hooks for camouflage netting on a pillbox.

All pillboxes would have been camouflaged. Many were dug into the ground or inserted into a hedgerow or hillside to provide the lowest possible profile; others had soil piled up on the roof and sides. Camouflage paint schemes and camouflage netting would be used to help break up the outline. Use was made of local materials: concrete made with beach sand, a covering beach pebbles, or stone from a nearby cliff was not only a time saving measure but aided camouflage by helping the defences to merge into the background.

In built-up areas pillboxes were disguised to look like a part of an adjacent building, carefully matched and provided with a roof to look as if they had always been there. In extreme cases, they were built inside existing buildings.

Some pillboxes were carefully constructed to resemble a quite different, innocent, structure: a haystack, a disused cottage, seaside kiosk, bus-stop shelter or railway signal box. It was not uncommon for pillboxes to be fitted with a dummy pitched roof to aid the deception. Some of these disguises bordered on the fanciful.

In some cases, the reinforced concrete roof was sculpted to make the distinctive form of a pillbox less obvious from the air.

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 and dummy pillboxes were constructed to confuse the enemy, as they were in France in 1940.

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." [Leonard Thomas Piper, WW2 People's War]

The Underground Propaganda Committee (UPC) was formed to pursue an anti-invasion whispering campaign by generating false rumours codenamed Sibs (from Latin: sibilare, to hiss). 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. Shortly after this rumour was released, it was given extra credibility when the RAF used incendiaries to attack a battalion of German soldiers on a practice invasion exercise. Burnt bodies were later washed up on the coasts of both France and Britain. Burns victims were sent to Paris and Berlin for treatment and were seen by many: American broadcaster William Shirer reported long hospital trains in Berlin, most of the men suffering from burns. The interrogation of a captured Luftwaffe pilot revealed that the existence of such weapons was common knowledge. The rumour seemed to take on a life of its own and documents found after the war showed that the German high command were completely taken in. 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 which, 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.

Would the defences have been effective?

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. 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; the ability of the German forces to land troops full equipped with all their heavy equipment in an opposed amphibious assault has to be doubted — at the time nobody had ever tried it before. 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. To even attempt a landing, local air superiority was essential, but even with that, whatever was left of the RAF would still have been able to operate over friendly territory while the Luftwaffe still had to fly a long distance to reach the English shoreline.

Most significantly of all, the British retained an ace in the form of the Royal Navy's British Home Fleet, a force that dwarfed anything the Kriegsmarine could put to sea. The British had 5 capital ships, 11 cruisers and 53 destroyers and many minesweepers and other smaller vessels, the German navy had just 1 capital ship, 1 cruiser and 10 destroyers. The home fleet was based far to the north at Scapa Flow and, in the event of an invasion would have sailed to the channel — possibly taking several days to get there. German plans called for the invasion fleet to be screened by blocking the channel with mines, U-boats and torpedo boats. While these 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 more equal terms than they had in the battle of France 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.

Destruction, neglect, rediscovery and reuse

Pillbox turned over and almost destroyed by coastal erosion.

The great majority of Britain's defences have been destroyed, a process that started even before the end of the war. Ditches and trenches have been filled; loopholes repaired; wood and metal re-cycled.

After the war, farmers, across whose land structures had been built were, in addition to receiving compensation, paid to fill in ditches and trenches and to demolish pillboxes. Today, hardly anything remains of the anti-tank ditches, but at the time they must have been the most conspicuous of all the fortifications; a few remain, much humbled, as field drains or field boundaries whereas others can be seen only as crop marks. In the case of pillboxes, the sum of £5 is sometimes mentioned to pay for demolition, but the challenge of demolishing such structures is considerable and it seems that most farmers pocketed the cash, treating it as compensation.

Today, it is very rare to find any part of Britain's defences other than that comprised of concrete. Immediately after the war, there were more pressing matters to attend to than conserving the detritus of a battle that never happened. For decades, with the sole exception of Pevensey Castle — where the new fortifications were seen as a part of the building's history — there was never even a suggestion that anything should be deliberately conserved.

As the years passed, erosion and modern construction destroyed many structures: at the coast fortifications have tumbled into the sea or sunk into the sands on which they were built; yet other features have succumbed to road improvements or have been demolished to make way for other modern developments. For those that remain, neglect and the attentions of nature have achieved a degree of camouflage that a soldier of the second world war could only envy.

Years after the war, memories faded and in the public mind it became popular to assume that the few pillboxes and other concrete objects that could easily be seen were all that was done to defend Britain; that their purpose was just to bolster morale and that there would have been no realistic hope of resisting a German assault. Even the Home Guard came to be seen as something of a joke as exemplified by the BBC sitcom Dad's Army. Whereas, in fact, what can be seen today are just the most visible and robust remains of what was a massive programme of fortification that was likely to have proven highly effective.

Extant war-time records are fairly poor, and nobody could be sure how many pillboxes and related hardened field defences had survived — or indeed, how many had been constructed in the first place. In the late 1970s, journalist Henry Wills began research on the topic eventually leading to publication of Pillboxes: A Study of UK Defences in 1985. Interest was stimulated, both public and professional; local surveys were carried out. Surveys culminated in the Defence of Britain Project which took place from 1995 to 2002 attempting to record all known military defence sites. From this and other surveys, it is estimated that some 28,000 pillboxes and other hardend field fortifications were constructed in the United Kingdom of which about 6,500 still survive.

For many pillboxes, a new use has been found. The type 28s, being internally spacious and having a large rear entrance are probably the most amenable to reuse and on farms and in gardens they serve as cattle sheds and storage lockers. Other, more imaginative pillbox applications recorded include use as a pub cellar, a conversion to a ladies toilet and an open-air theatre box office.

Some pillboxes have been converted to make roosts for bats. Pillboxes that are well dug-in and thick walled are naturally damp and provide a stable thermal environment that is required by bats that would otherwise hibernate in caves. With a few minor modifications, suitable pillboxes can be converted to artificial caves for bats.

References

• Alanbrooke, Field Marshal Lord. War Diaries 1939-1945. Phoenix Press, 2001 ISBN 1842125265.

• Cruickshank, Dan. Invasion — Defending Britain from Attack. Boxtree, 2001 ISBN 0752220292.

• Foot, William. Beaches, fields, streets, and hills ... the anti-invasion landscapes of England, 1940. Council for British Archaeology, 2006 ISBN 1902771532.

• Lowry, Bernard Lowry. British Home Defences 1940–45. Osprey Publishing, 2004 ISBN 1841767670.

• Willis, Henry. Pillboxes: A Study of UK Defences. Leo Cooper. 1985 ISBN 0436573601.

• Ruddy, Austin. British Anti-Invasion Defences 1940–1945. Historic Military Press. 2003 ISBN 1901313204.

• 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.
• Whispers of War - The British World War II rumour campaign. Disinformation in defence of Britain.
• 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.