In two of my novels, I created scenes set in WWI trenches. To make them as realistic as possible I needed to understand trench layouts and the nomenclature involved. I found a few diagrams on various sites and in one of my non-fiction books.
(1) There are front line trenches and support trenches as well as interconnecting alleyways – called communications trenches.
(2) Artillery is in behind, firing over the heads of their troops.
(3) All trench lines zigzagged in part to prevent explosions from rippling sideways – and hence wounding or killing more soldiers – for more than a short distance.
The second diagram (source: Vimy Ridge 1917, Osprey Publishing) sets out the concept of a platoon attack against its objectives.
(4) Troops are deployed in waves. Note the planned 1st Wave and 2nd Wave troop deployment.
(5) riflemen and bombers in front (1st line),
(6) rifle bombers and Lewis gunners in behind (2nd line)
(7) and finally moppers up (3rd line) charged with the responsibility of guarding the entrances to dugouts and communications trenches.
A third photo – also taken from Vimy Ridge 1917, Osprey Publishing – is an artist’s depiction of a German trench. It would have been critical in battles like Vimy Ridge for attacking troops to know something of the layout of German trenches.
Apparently German trenches were often better established than British and French ones and had more reinforcing structure.
(8) Troops sheltered in the deep dugout, the entrance of which we can see at the top right, during preliminary bombardment. Months of rain often left trenches waterlogged.
(9) Two men on the ledge operate a Maxim gun; one man firing the other feeding ammunition. They stand on what’s called the fire step. Two other men carry boxes of ammunition to resupply the machine gun which is capable of firing 500 rounds per minute.
(10) The dead man was likely in charge of sighting the Maxim gun, a task requiring him to look over the parapet.
Perhaps more than you wanted to know about trenches!