British hardened field defences of World War II
British hardened field defences of World War II were small fortified structures constructed as a part of British anti-invasion preparations. Included in the definition of "hardened field defences" are the structures popularly known as pillboxes, a reference to their shape as well as other concrete weapon emplacements such as anti-tank emplacements.
Background
With the German invasion of Low Countries in May 1940 came the realisation that the United Kingdom was vulnerable to invasion. Late in May 1940, the Chiefs of Staff Committee decided that vulnerable beaches needed to be fortified with pillboxes and anti-tank obstacles. This proposal was resisted by the Commander-in-Chief, Home Forces, Sir Walter Kirke, who favoured a mobile reserve to counter invasion, but shortly afterwards, he was replaced by Sir Edmund Ironside. Having very few tanks or lorries to form such a reserve, Ironside formulated a plan to have a "coastal crust" of defended beaches, backed up by a network of "stop lines" which would limit any incursion, with localised defences for "vulnerable points" such as airfields. Work on these defences continued through the summer of 1940, until in late July, Ironside was replaced by Sir Alan Brooke. By then, there were more resources for mobile defence and work on fixed defences became a lower priority, especially the stop lines which Brooke disliked. In February 1941, British General Headquarters issued an order that no more pillboxes were to be constructed. By then, some 28,000 hardened field defences had been constructed; about 25 per cent of these have survived.Design and development
In May 1940, the directorate of Fortifications and Works was set up at the War Office under the direction of Major-General G. B. O. Taylor. Its purpose was to provide a number of basic but effective pillbox designs that could be constructed by soldiers and local labour at appropriate defensive locations. In the following June and July, FW3 issued six 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 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.
Embrasures were available 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.
The degree of protection offered by a pillbox varied considerably: the thickness of the walls and roof generally varied from just 12 in to 3 ft 6 in or more although the commercially produced designs were often much thinner. In March 1940, General Brooke carried out penetration trials and recorded that a anti-tank gun could easily penetrate up to of reinforced concrete. Despite such results, the thick-walled pillboxes were designated as shell-proof, whereas the thinner-walled pillboxes were designated as bulletproof.
Internally, pillboxes are generally cramped and spartan. Some internal concrete shelves and tables were provided to support weapons and some were whitewashed inside. Only the [|Type 28s] provided a little space—sufficient for a few home comforts.
Adaptations
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 free standing blast wall or a steel door.Appearance also varied due to the building materials used, although all the FW3 designs 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 and/or corrugated iron. Wood shuttering was removed, whereas corrugated iron was sometimes left in place. Construction often took advantage of whatever materials were available locally and this expedient 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, several instances are known where scrap metal had been used such as parts of an old bed or park railings.
Local commanders introduced modifications to the standard FW3 designs or introduced designs of their own, which were sometimes produced in some numbers and in other instances were completely ad hoc designs suited to local conditions. Other designs were produced as commercial ventures. Finally, there were a small number of pillboxes that had been constructed in the first world war.
FW3 pillbox types
The approximate numbers of extant pillboxes of each type are given based on data from the Defence of Britain database, records from County HERs and submissions to the UK Pillbox Study Group.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 long and it was generally built to the bulletproof standard of thick, although shellproof versions with walls around thick were also built such as the granite and concrete examples on the Cowie Line in Kincardineshire and along the upper Thames in Oxfordshire. Internally, there is a Y- or T-shaped anti-ricochet wall ; the internal wall also helps support the roof.The Type 22 is the second most common pillbox type with 1,347 recorded as being extant. It is easily confused with the common Type 24, which is an irregular hexagon, and the less common octagonal.
Type 23
The type 23 pillbox is rectangular in plan – essentially two squares, one of which is roofed and the other open – with embrasures 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 through a door to the covered section. The walls were wide by long and usually built to a bulletproof standard of thick.The type 23 is uncommon; 87 are recorded as being extant. A further variant exists in Lincolnshire consisting of a double-chambered type 23 with an access door with anti-aircraft gun mount and a chamber on either side, known as the [|Lincolnshire three bay].
Type 24
The type 24 pillbox is an irregular hexagon in plan. The rear wall is the longest at about ; this has the entrance with an embrasure on either side. The other walls vary from , 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 internal wall also helps support the roof. The type 24 was always built to at least bullet-proof standard of thick, but often was thicker.A thick-walled variant was introduced to a shellproof standard; it was larger externally and had walls thick. This thick-walled variant is sometimes called a Type 29 by pillbox researchers but this is not an official designation. In a variant on the Scottish Command Line, the entrance was moved from the long wall and the two rifle embrasures were increased in size to allow a Bren and Boys Anti-tank rifle to be mounted side by side.
An unusual local variant of the Type 24 can be found along the River Wey in Surrey between Godalming and Albury. Known as a Mowlem Drum after the contractor that built them, these are Type 24s that have had circular external shuttering used to produce very thick walls. Internally they are identical to a standard Type 24. Most are fully circular but some still have the flat rear wall of a normal Type 24 allowing the two rear embrasures to be present. There are 25 examples of this type still extant.
The type 24 is the most common type, with more than 1724 recorded as being extant.
Type 25
The type 25 pillbox is the only FW3 design that is circular, with a diameter of. The walls were just 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 30 are recorded as extant.
Type 26
The type 26 is a simple square in plan, each wall being long. There is a door in one side and embrasures in each of the remaining three walls with, possibly, an additional 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 bulletproof standard at about thick.The type 26 also had an important prefabricated variant, in which the shuttering – both inside and out – was provided by precast concrete slabs slotted into reinforced concrete posts. The shuttering was filled with concrete in situ. This pillbox was also known as the 'Stent' after the company that produced the prefabricated components, Stent Precast Concrete Limited. On those examples where damage allows inspection of the construction, it seems that the concrete fill was not reinforced.
The type 26 is uncommon: 140 are recorded as extant, including the Stent prefabricated type.