I recal reading somewhere that one of them had its own battalion of troops attached.
Is it still there?They were a massive waste of resources when they were sorely needed elsewhere. Their effectiveness was also called into question. When the firing rate is a few shells a day why bother. It also took a few months to set them up.
My Dad was on the receiving end of one of the smaller rail guns at Cap Gris-Nez. After the invasions the Germans would pull it back through the tunnel and turn to vertical fire. Dad and his mates slept under a barn door which they took with them on their truck. Woke up one night with a piece of shrapnel from one of the shells of the gun that had gone through the door. Just stopped short of his noggin. The yanks sent over a raid of Fortresses which buried the Germans and their gun in the tunnel.