The Munich Crises of September 1938, when War seemed imminent, led to hectic trench digging in public parks and other open spaces for protection of the population against air raids. These were either unlined or lined with timber. After the crises, many were in filled (e.g. at St Felix School, Southwold). At the outbreak of war many were hurriedly repaired and retained as a permanent feature throughout the war, with a standard design of concrete trench lining issued.
Above: Example of a timber lined shelter dug during the Munich
The standard concrete lined trench shelter was actually extremely vulnerable to damage caused by a bomb exploding in the ground. The precast concrete lining units consisted of side panels which stood in slots on a floor with a similar roof unit resting on top. If assembled correctly they could withstand the pressure of the earth. A bomb that exploded in the ground caused a permanent movement in the earth and if it exploded in close vicinity to the shelter these pressures proved excessive, causing an inward displacement of the side panels with the shelter collapsing a result.
Right: Plan of standard concrete trench
lining and examples of how it could be
displaced by near misses.
As a result designs were issued to reinforce concrete lined trenches, either with a rectangular steel frames at six foot intervals connected by longitudinal members or building reinforced brick / concrete baffle walls at intervals and supporting the longitudinal members on these walls. The cost of carrying out such reinforcing works was met by Government grants.
Ipswich Emergency Committee minutes note both unlined trench shelters and shelters lined with wood in use during the War. A scheme was drawn up to replace some of the timber lined trenches with concrete linings. Certainly some of this work was delayed due to a shortage of trench linings (production of the linings was being held up due to a shortage of steel needed for the reinforcing). Some shelters were only part concrete lined.
By 1944 dampness in trench shelters was a problem. Many timber shelters were not water-tight and the timbers in poor condition. Some concrete shelters were also damp due to excessive condensation. Many bunks in the sheleters were damp and unsuitable for sleeping on. As people were still using shelters as dormitories on an "Alarm" or "Alert" this caused concerns for public helath.
As well as communal trench shelters, many households also dug trench shelters in their gardens, some which even show up in aerial photos of the time. Pamphlets were also issued on the digging of slit trenches for air raid protection.
Enterprise versus Bureaucracy – The Development of Structural Air-Raid Precautions during the 2nd World War, Lord Barker of Windrush, O.B.E., Sc.D.,F.R.S., C.Eng, Pergamon Press 1978
Contribution to Victory, F Rowlinson, MV Electrical Co Ltd, 1947
Various correspondence on shelters, SRO