At Verdun the French are preparing to launch an attack on Fort Douaumont. They have been shelling the fort and surrounding German trenches for the last few days, but today they open up with a new weapon, a gun that can fire monstrous 400 millimetre shells. The fort has been so battered by French artillery that it is no longer the impregnable fastness it once was. Now the 400 mm shells rip into the fort itself, wreaking havoc among the defenders. They retreat to the lower levels, but when a shell penetrates into the depths, setting off a fire near to a shell store, their commander decides that discretion is the better part of valour. A few men stay behind to battle the flames but when they run out of water they too leave the fort.
So the great Fort Douaumont now lies empty and undefended. Or almost undefended. In the rushed evacuation, two sentries in an isolated gallery far from where the shells were landing were forgotten. They remain at their post, defending the fort on their own.