The purpose of a road block was essentially to ensure the protection of Home Forces within a particular area, whether it be from enemy armored columns or parachute troops for example. The delaying power of a road block would be limited unless it was covered by effective fire of the defence. A road block would produce maximum effect if it was encountered unexpectedly by the enemy in places where a deviation round it was difficult. Of importance was whether the road was need for access to Home Forces for counter attack in which case the block would have to be able to be removed quickly.
From 1939 up to the summer of 1940, road blocks were more or less improvised using any materials at hand (eg carts filled with rocks, sand bags etc). Such improvisation and lack of co-ordination would have meant the blocks would have only had limited effect. In one Division War Diary mention is made of a ‘staggered’ road block. The block consisted of staggered sand bagged breast works or any other available material that would not be easy to remove. The distance between the breast works was to be about 40 yards. The block would be closed by placing Dannert Wire (with a suitable holding e.g. ‘knife Rests’) from the breastwork to the other side of the road. Instructions from 11 Corps soon banned the construction of ‘staggered’ blocks as they would impede the movement of any reinforcing troops.
Above: Left staggered road block - soon prohibited by Home Forces. Middle: Artists drawing of Dannert Wire block. Right - danger of uncordinated road blocks - the enemy could simply go round them is in this blcok in France during the summer of 1940.
Many types of road blocks were designed including concrete cylinders, ‘buoys’, 90-lb rail or RSJ blocks and bent rail blocks. A very simple idea from the commander of 6 A.A Division, Eastern Command was a curtain made up of hessian or any non-transparent material. This would be stung across a road, high enough to prevent a tank seeing over it. This would force the tank to halt (when it could be attacked), divert off the road (onto a minefield) or charge the curtain which would snag over the tank blinding it. It was forwarded to GHQ and may be the origin of the suggestion in the MTP on Obstacles and the Home Guard Handbook that obstacles should be screened with canvass screens to casue delay as without reconnaissance the enemy would not know what kind of obstacle , indeed if any, faced him. It would also prevent the enemy taking aaurate aim at the most vulnerable part of the obstacle. As with other anti-tank obstacles there were extensive trails to assess the effectiveness of each obstacle. Trials at Imber on 5th-7th December showed that both 90-lb rail, bent rail and concrete cylinders were effective obstacles but buoys were not. However another trail on May 13th 1941 stated the importance of reducing the speed of attacking tanks as low as possible to make rails effective. All of the above obstacles were movable – they would often be backed up with solid blocks on the verges (e.g. concrete cubes, pimples etc).
Above - Bent Rail Block.
Right - Rail and Cylinder Block.
It would appear to some degree that the various Commands adopted different obstacles, for example Southern Command was supposed to have opted for buoys to a large degree, while for 11 Corps (Suffolk area) the 90-lb rail is by far the most mentioned block in Home Force war diaries.
11 Corps issued guidance for which roads were to be blocked and the type of block:
Inner defence of port areas and the sea front –permanent blocks proof against 36 ton tanks.
To prevent enemy egress – demolitions.
Beach exists - permanent blocks proof against 36 ton tanks.
Within 5 miles of beaches – permanent blocks against 36 ton tank and demolitions
Tank proof localities – semi-permanent blocks proof against 6 ton tanks
Road centers – permanent blocks proof against 36 ton tanks if within 10 miles of suitable tank beaches, otherwise proof against 6 ton tanks.
Tank defiles – temporary blocks
Approaches to aerodromes – permanent blocks proof against 6 ton tanks within 5 miles of aerodromes
G.H.Q. Line and Command Line – permanent blocks proof against 36 ton tank and demolitions.
Permanent Blocks were to be constructed so that any traffic moving forward to deal with any air or sea borne landing could pass unheeded but could be made effective in a very short space of time. Such tank proof blocks were to be 5 ft high. On “Essential Traffic Routes” a gap of at least 20 ft should be left, to be blocked by steel rails when required. However some specified key routes were not to be blocked or have Check Points established (although all roads crossing or joining such routes were to be blocked). On other roads the gap should have a minimum width of 13 ft. Suffolk Sub-area further stated that road blocks were to be either permanent road blocks (all blocks at nodal points or on the crossings of the Command line using rails, bent rails, or cylinders) or temporary road blocks (all others).
Numerous permanent road blocks were constructed by the Army in Suffolk from July onwards consisting of concrete blocks and steel rails covered by a pillbox or sandbag post. It was often noted the pillbox was often not well sited and sandbag posts were too obvious and would draw enemy fire. The War Diary of 46 Brigade (15th Division) makes reference to the use of the bent rail block to be used on rail bridges or access points to rail lines, to prevent the enemy from utilizing these routes to gain entry into defended localities - this block replaced the use of waggon blocks.
The standard policy for road blocks in Suffolk in the forward sub-sectors was that they should be closed on ‘Action stations ‘then reopened once the local commander was confident that the block was effective. It would only be then closed on the approach of the enemy and be capable of being reopened in five minutes once the threat had passed. One rail should be left out to allow the passage of motorcycles. Troops were expected to practice regularly in opening and closing blocks.
Suffolk Sub-area issued instructions that permanent blocks were to be closed on ‘Action Stations’ then reopened when the commander was satisfied they were effective. Temporary blocks were not to be closed on ‘Action Stations’ (although the local commander would check material for the block ready for use at a moments notice) but only when the enemy was within striking distance of the block. Temporary Blocks would be consructed from any availbale material to the local Home Guard in 'Keep' villages/Hold up Villages etc.
From 1941, with the introduction of tubular scaffolding, reference is made in Home Forces war diaries to the use of Z1 scaffolding as a road block in Suffolk (see Defence Works - Tubular Scaffolding). Such blocks would have extended into the road verges to allow anchor pickets to be driven in. Sockets in the road surface would also have been made to anchor the road block.
9th Lancs papers, TNA
15th Div papers, TNA
164th Brigade papers, TNA
1/6th Lancs papers, TNA
46 Brigade papers, TNA
Scheme of anti-tank obstacles for defence of Great Britain, TNA
Field Engineering (All Arms) MTP No 30 Part III: Obstacles, The War Office, 1940