During 1940 the defences built against invasion were intended to “hold up enemy forces landed by sea or air”. They were also designed to “meet the weapons which the enemy is most likely to bring”.
GHQ considered it unlikely that defences in Britain would have to be able to withstand the deployment of heavy guns as was the case on the Continent. Such guns would almost certainly be tractor drawn equipment. Such equipment would unlikely be available to parachute troops or airborne troops. Neither would they be likely mounted in light or medium tanks, which would probably be the first to be landed by sea.
Many pillboxes were only bullet proof as this was considered sufficient to withstand most of the weapons likely to be deployed against them during the initial stages of invasion.
As early as August 1940 the question of pillbox reinforcement was raised. The minutes of a conference on Defence Policy, Eastern Command noted that key pillboxes were to be 3’6” thick, the remainder 15”. The minutes also note “Where 15” pillboxes are to be brought up to 3’6”, only those sides which are liable to attack by gunfire need be strengthened.”
By 1941 GHQ had became concerned that pillboxes were obviously not proof against high velocity anti-tank weapons. A paper submitted to the War Office noted two forms of attack that defences would have to deal with:
Where the enemy’s scope for the deployment of tanks and heavy guns was limited – e.g. in the first stages of invasion.
Defence against a deliberate and fully-mounted attack.
It was noted that the first phase would invariably develop into the second phase, the conclusion being that defences should always be developed to meet the deliberate attack and pillboxes should be designed to withstand all modern weapons.
A Research Board carried out trials on reinforced concrete that would be required to stop a 6 pounder shot. The Board also felt confident in calculating the requirements needed to stop the German 88mm.
A pillbox capable of stopping such weapons would need to be likely 6- ft thick. Existing pillboxes could also be strengthened to a degree. It was recognized that such work would require a huge amount of labour and materials, both in short supply. It would not be possible to carry out such work in all Commands simultaneously so it was recommended that priority be given to Southern and Eastern Commands on vulnerable areas. The Chief Engineer GHQ recommended that the following level of protection should be provided:
(a) Protection in the walls to meet an attack by an 88mm gun at 500 yards allowing for the impact of six shots in a 6-ft square.
(b) Protection in the roof to withstand a 250 kilo bomb.
First priority to be given this level of protection was anti-tank gun pillboxes with L.A emplacements to be second priority.
As a result of the recommendations, the Commander in Chief directed that first priority would be given to anti-tank gun pillboxes on beaches in the specially vulnerable areas of Dungeness, Dover to Ramsgate in Southern Command and Southwold in Eastern Command. Both Southern and Eastern Command were asked to review their requirements in this matter and to submit proposals for improvement of pillbox defences. This could either be new pillboxes or strengthening existing ones. The following details were to be provided:
(a) Serial No
(c) Outline plan and elevation of existing pillbox, including loopholes and requirements of new arcs of fire if required.
(d) For new pillboxes, an outline plan, type of loophole required and arcs of fire. Walls should be 6-ft thick.
GHQ emphasised that this was a long term programme with no prospect of completing even a very limited number in the immediate future.
Eastern Command noted that there were no anti-tank gun pillboxes in the Southwold area but submitted details of nine existing pillboxes in Southwold, one at Dunwich and one at Minsmere to be strengthened and a new pillbox to be constructed at Walberswick. Despite the fact that Corps and Commands submitted a list of their requirements, the Board’s research still had not reached the stage for practical pillbox design. Two designs were however produced by F.W.3 (drawings No 45 and 46) and issued by the War Office. It was noted that these designs were not the special case on which the Research Board had been working on – a pillbox proof against any type of gun. War Office drawings No 45 and 46 were for anti-tank gun pillboxes to be used on the coast. It was to have a 6 ft thick wall on the exposed flank, with 3 ft 6” thickness on the other walls and a 1 ft 6” inch roof.
Right: Map showing pillboxes identified by Eastern Command
in Suffolk which were to be strengthend along with a new
pillbox to be built at Walberswick - 1941. This work was
almost certainly not carried out and by 1942 the pillbox was
seen redundant as a defensive work.
As already noted, existing pillboxes could also be strengthened. Bullet proof pillboxes (i.e. 1 ft 6 in thick) could be increased to 3 ft 6” thick. Designs for this work could be prepared locally. The main principle to be followed (per GHQ memo dated 11 Sept 1941) was to add a reinforced concrete wall on the “vulnerable side”. If existing loopholes were no longer required a key for the new wall could be obtained by filling them up. The wall could either be bought up to the height of the roof but this would then require cutting out new loopholes or a compromise could be adopted and just bring the reinforcement up to the level of the existing loopholes.
Above: Left - one of three designs issued by the War Office for strenghening existing pillboxes. This work has been carried out on the above
Type 24, RAF Bawdsey.
A further memo from GHQ dated 26th Oct 1941 noted that the principles of strengthening existing pillboxes should now be:
The wall on the ‘enemy side’ to be increased to 6 ft thick to the full height of the pillbox and contain no loophole.
Other walls to be increased to 3 ft 6 in thick up to loophole height. GHQ produced three suggested designs for this.
No pillbox to have more than one loophole per 70 sq ft of floor space.
Roof to be increased to 1 ft 6 in thick.
As this would change the existing field of fire, Field works would be required to cover the front of the pillbox.
As well as reinforcement, GHQ recommend a further improvement to pillboxes in 1941 – “In general, opportunity should be taken to eliminate many of the redundant loopholes with which the earlier types of pillboxes were “riddled”. What may be called the “sieve” type of pillbox is nothing but a death trap”. In Suffolk, 54th Div drew up a list of 127 pillboxes in which some loopholes were to be blocked.
Right: 'Suffolk Square' pillbox which has been
'strengthened' by the blocking of loopholes. In
this pillbox a Turnbull mount has also been
An alternative to concrete works capable of withstanding determined attack was the small steel machine gun post distributed in depth as found during the last year of the Great War – the Hobbs casemate. This was basically a steel cupola mounted over a 3ft 9 in pit with only 18in showing above ground level. The rationale for this was the age old problem of gun and armour – the gun would always win in the end. Even the Maginot type of fortification was not impregnable. These small posts were inconspicuous, easily hidden and were bullet and splinter proof. It would be hard for a tank to hit except at short range. GHQ noted that a number of similar designs existed at the War Office and were worthy of further trial. They would require less steel per weapon to be protected than reinforced pillboxes. They were designed to fit into a system of field defences. Presumably the Tett Turret and Allan Williams Turret were examples of these designs. The idea was never really taken up as so few of these structures were constructed.
The design for the Tett Turret was a rotating steel turret mounted onto a sunken concrete pipe but the only known examples (including one at Sudbury, Suffolk – now destroyed) actually had concrete turrets. It could incorporate two rifle men or a Bren gunner and his number two. It was primarily designed to defend road junctions, its lower profile than a pillbox being its main selling point. It proved too cramped and it was argued a slit trench would provide similar protection so only a handful were ever constructed.
The Allan Williams Turret consisted of a steel cupola mounted over a sunken pit. It could be rotated through 360° and had mounts for Bren and Lewis light machine guns and the Boys anti-tank rifle. Of the 199 ordered 11 Corps, Eastern Command, received 116.
Above: Left - sketch for the Tett Turret. Right - Allan Williams Turret
Pillboxes – A Study of U.K Defences 1940, H Wills, Leo Cooper, 1985
Pillboxes of Britain and Ireland, M Osborne, Tempus, 2008
Construction of Pillboxes, TNA
Chief Engineer, GHQ Home Forces, TNA