The main gallery
It connects the Ammunition Entrance to the around one mile away Combat Blocks. Along it runs a 60 cm wide track for loco-tractor drawn carriages, fed by overhead wire carrying 600 volts. This small train was solely used for conveyance purposes between the front and the rear.
On this gallery are : a secret emergency exit, the drain water outlet and the morgue, drilled intake points for electric and telephone cables, the Command Post, the front sub-station and a water cistern, for fire emergency.
The emergency exit was meant to enable such men as were blocked in the gallery to be able to leave the bunker. A ladder within a shaft, whose upper part was filled with gravel to deny the enemy the way down, could take them up and out into a wood. In the lower part of the shaft, two pits run parallel for the gravel to fall down into one of them and the men to climb further up the ladder in the other, on opening the trap half-way up.
The two ends of the main gallery gently slope down to their middle, where a sewer collects the water flowing along a gutter. The sewer opens into a 240 m long gangway, from which the water drains out into the open, then down a woody slope. This channel could also be used as an emergency exit.
The morgue was meant to hold some coffins, in the heat of a battle, pending their removal. As it was deemed vital to keep up liaison with the outside, telephone and electricity wire intake points were dug into the wall of the gallery, where they could but hardly be spotted out.