SMHS project: Slit trench


11 Mar 2012

Whilst working at Cripp's Corner, the vineyard owners kindly gave us permission to undertake some experimental archaeology, in the form of a slit trench reconstruction.

Slit trenches were the most numerous defence work in Sussex during the Second World War and are often overlooked. The most common design was a two-man trench that acted as a firing position while providing cover from bombardment.

Slit trench

Slit Trench design

In order to better understand this type of defence we undertook to construct one using British Army manuals of the period.

The trench is six feet long by 2 feet wide (1.8m x 60cm) and 4.5 feet deep (1.4m). A drainage sump in the floor adds another 2 feet (60cm) to the depth.

Revetment was essential to prevent the walls of the trench collapsing in. Any suitable material could be used, from brushwood to corrugated iron, if available.

The revetment was to be held in place by wooden stakes or iron pickets driven in and anchored using wire.

Something we were interested in was the amount of time it would take to dig a trench; according to a 1944 manual, one man should be able to excavate a slit in 3-8 hours (minus sump and revetment), using pick and shovel. The nature of the ground would have a bearing on the time taken.

Our reconstruction

We wanted our trench to be as authentic as possible, down to the time taken to construct and the materials used.

We were also aware that a measure of improvisation would be required, particularly in using whatever materials were available to hand.

Excavation

Two men were employed in the digging task, taking it in turns with pick and shovel, and disposing of the spoil. This latter point is perhaps what surprised us the most. The manuals state that spoil had to be removed to prevent it casting shadows and revealing the location of the trench to the enemy. Just shovelling our spoil about 3m away was an exhasting and labour-intensive task.

The local geology was not helpful; below the topsoil were layers of sandy clay and a particularly hard layer of ironstone that had the pickaxe bouncing out of our hands. A second layer almost had us stopping short of reaching the regulation trench depth, but we persevered.

In all, the excavation took us about six hours, with two people taking turns to excavate and shovel the spoil away.

Revetment

Revetment material proved simple to source; dismantling a long-abandoned treehouse provided some sheets of corrugated iron. These proved surprisingly easy to bend to shape and drop into the trench.

The problem was that of anchoring it in place according to the prescribed method. Despite having foraged some suitable tree branches to use as stakes and salvaged a piece of angle-iron from a scrap pile, all attempts to drive stakes through the ironstone failed.

Slit trench

Having finally been defeated by the rocky strata, it was decided to improvise a solution using locally-sourced materials. We therefore decided to cut some thicker lengths of wood and use them to strut the trench from inside instead.

Durability and Maintenance

Having completed the slit trench as close to the military specifications as possible, the reconstruction was not yet over, however. We also wanted to see how durable the trench would be, in terms of drainage and collapse.

We revisited the trench after a few weeks and found that heavy rain had flooded it two feet deep! The sump had worked, but the clay, not surprisingly, was holding the water. The trench wall on one side had also suffered subsidence behind the corrugated iron revetment.

A few weeks later and we found that the floodwater had been absorbed into the clay, making a thick, stodgy Somme-like mud that was almost impossible to walk through. An hour was spent scooping out the mud and effecting repairs; soil had to be shovelled down the back of the revetment on one wall to shore up the trench.

It had originally been planned to keep the slit trench open to allow visitors to see the sort of defence works that would have been manned by those confronting the invader. However, although our repairs had been effective, another site visit a few weeks later confirmed that a slit trench requires regular maintenance beyond our capacity. We therefore decided to backfill the trench for safety reasons.

Conclusions

Although it was disappointing to undo all the hard work, it should be remembered that a slit trench was rarely intended to be a long-term structure. Constructed in a few hours, a trench might become redundant as the situation on the front line changed and fresh trenches dug as an army advanced or withdrew. Short of revetting our trench in brick or concrete, to have tried to preserve it for more than a few weeks without disproportionate effort to maintain it would have been an artificial situation.

This piece of reconstructive archaeology was well worth the effort though; we learned a lot about fieldworks as a result!


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