Manual of Field Engineering 1933 notes that slit trenches “are useful to give protection from shelling and aeroplane bombs”. Experience in France had shown that slit trenches were a “complete answer to dive bombing” – 1st Liverpool Scottish Operational Instruction No 27. This Operational Instruction notes that that “the importance of having slit trenches in billets, camps or barracks cannot be over emphasized”. There is frequent reference in Home Forces War Diaries for the need to dig slit trenches for protection against enemy bombing (referred to as Passive air Defence -PAD ) at billets, field gun positions etc.
Slit trenches should be about 3ft wide at the top and 4ft deep. They were normally dug to hold between 10 and 25 men and should be dug in a zig-zag pattern, revetted and drained.
Left: Slit trenches, MTP No 30, 1941
Right: One man slit trench
From about 1942 onwards the slit trench was also used in defensive works (the Weapons-slit )as the Fire trench was considered valueless against air attack. However the use of slit trenches in anti-invasion defences was probably limited to holes from which Molofoff cocktails could be thrown from as the Fire trench was still the standard defensive work in 1940. Many Weapons-slit systems dug as part of training from 1942 onwards can be found on some of Suffolk’s heathland.
Above: Stages in digging a weapons-slit and cross section of a V shaped Weapons-slit.
Above left: Plan of a platoon post consisting of Weapons-slits linked by Crawl trenches. Right: GPS plan of a weapons-
slit and Crawl trench system dug for training, Westleton Walks.
Manual of Field Engineering (All Arms) Vol I, HMSO 1933
Field Service Pocket Book, Pamphlet No 7 Field Engineering, WO 1944
1st Liverpool Scottish papers, TNA