In this aerial photo, a portion of an old reserve trench is visible near the Somme River, on the western front, in France.
By 1918 this kind of trench system had fallen out of use by both sides on the Western Front and trenches like these were abandoned.
I wonder what the theory behind the trench layout is, especially the crenellations. Providing blind corners to hide/fire round if the enemy gets in the trench, or a mortar explodes in it? Increasing the field of fire from the forward sections? More men per linear length of front? Civil engineering issues?
That crenelation in the front line trench is what’s called a traverse and there’s a few reasons trench systems were built with them.
Primarily they’re defensive and they reduce casualties to the defenders. They provide an obstacle for the main killer on the battlefield, artillery. It stops blasts from travelling far when a shell hits and does the same for the deadly shrapnel or shell splinters.
When an enemy does get into a trench they also provide for a useful defensive barrier for defenders as well as stopping an enemy from firing down the entire length of a trench, called enfilading.
Small, sharp traverses like that were mostly done on the very front line trench, where an enemy’s bombardment would be heaviest. But as you can see below, pretty much every trench had some level of traverse.
For a quick breakdown of a trench network.
1. Front line trench, also known as a firing trench. Has the most obvious traverses as soldiers here are going to need the most protection. Not usually held in huge numbers, but varies depending on a ton of factors. Connects to support trenches with numerous communications trenches to facilitate easy movement.
2. Support trenches. Usually one, but sometimes more lines of trenches close to the front line trench. Usually has large dugouts, machine gun posts and other supporting troops. Often has baffles or dead ends built into it to confuse enemies.
3. Communication trenches. How everything and everyone gets into and out of the front lines.Fewer of these ones connecting the reserve trenches and support trenches.
4. Reserve trenches. Where reserve troops are held, in case of an enemy attack or in preparation for an offensive operation. Also where battalion headquarters and support units such as field kitchens were located.