A report from MI 10 circulated on Jun 14th 1940 listed the methods by and the types of tanks that the enemy might land in Britain. By land plane it was thought that tanks landed would not exceed 6 tons and 15mm of armour and would easily be put out of action with anti-tank rifles. Tanks landed by seaplane would not exceed 9 tons and 25mm of armour, which would be proof against anti-tank rifles although the tracks would remain vulnerable to such weapons. Tanks landed by barge would include the heaviest tanks the enemy possessed (in 1940 this was the Pz V/VI at 36 tons). The report listed obstacles that would temporarily halt tanks landed by the above methods.
Above: Obstacles for tanks landed from various sources
Right: Standard tank blocks, Field Engineering and Mine Warfare, Pamphlet No 2, W.O. 1951
As home defences developed, the most common concrete anti-tank obstacle used were the cube, pimple and coffin. The concrete cube was a recognized obstacle from at least 1925, with two foot cubes given as an example of an anti-tank obstacle in the 1925 Manual of Field Works. The standard anti-tank obstacle used on Suffolk’s beaches was the 5 ft cube, although much larger cubes can be found at Bawdsey and the occasional 3 ft cube can still be found (e.g. Dunwich and Sizewell). Most of the surviving beach cubes are a single linear line with, for example at Walberswick, right angle spurs to prevent movement along the beach as well as inland of the beach. I am only aware of pimples being used inland and the coffin would appear not to have been adopted at all in Suffolk.
Cubes, Minsmere Dunes Cubes, Walberswick
'Pimples' on the Eastern Command line at Elmswell.
Extensive testing of the various obstacles was carried out from August 1940 onwards. The first trials showed that all concrete obstacles could be destroyed with 2 pounder shells. Crucially they demonstrated that smaller obstacles arranged in depth would take longer to destroy than single lines of larger obstacles. More importantly smaller obstacles would offer less cover to the attacker and would not obstruct the field of fire of the defender as much (the war diary of the 2/4 South Lancs, Jun 30th 1940, actually mentions cubes passing right in front of section posts!). As a single line of 5 ft cubes would require 78,000 cu ft per mile of concrete and a double line 156,000 cu ft per mile the recommended policy in August 1940 was to discontinue with the standard 5 ft cube.
However this would not seem to have been a universally adopted policy as trails on the 5 ft cube were sill been carried out in 1941. One such trail on July 30th showed that it would take 35 rounds of 2 pdr shot to destroy one reinforced 5 ft cube and 16 rounds of 25 pdr shot. Thus it would take a considerable amount of time and ammunition for a tank to shoot its way through such an obstacle. Interestingly these trials also showed no advantage in arranging cubes ‘corner ways on’. During this time the tank would be stationary and vulnerable to attack. As a result of such trails it was recommended that an obstacle of reinforced cubes ‘diluted’ with unreinforced cubes would provide a satisfactory obstacle.
Concrete cubes would seem to have been erected in large numbers during the summer of 1940 along the Suffolk Coast (for example the war diary of 558 Field Company RE states that 7153 blocks were constructed between May and November). Not all cubes were erected by the RE – the war diary of the 5th Kings (30th May 1940) mentions two officers going for instruction on the construction of blocks as battalion troops would have to carry out the work themselves.
The policy of discontinuing with the standard 5 ft cube seems to have at least been partially adopted in Suffolk. Operating Instruction No 3, 15th Scottish Div, 18th March 1941 states that displaced cubes on the foreshore will not be replace but the gap filled with mines. The war diary of the 6th K.O.S.B states that cubes were actually removed to improve the field of fire (diary entry 28th March 1941). From 1941, with the introduction of scaffolding, beach obstacles became a complex obstacle combining wire, mines, cubes and scaffolding.
Anti-tank Cubes, Sizewell. These were incorporated into a
complex obstacle involving scaffolding, mines and wire.
Schemes of anti-tank obstacles for the defence of Great Britain, WO199/54 NRA
Experiments with anti-tank obstacles, WO199/1722 NRA
15th Div papers, NRA
558 RE Field Coy papers, NRA
6th K.O.S.B papers, NRA
5th Kings Regt papers, NRA
2/4 South Lancs papers, NRA
Suffolk’s Defended Shore, C Hegarty & S Newsome, English Heritage, 2008