This is a glitch for Allies.

At the main entrance to the chateau there are boxes and so on but there is also a lorry/open top van at the bottom of the bridge.

Get onto it by using the front right side of the lorry and jump until you get onto the open top part of the lorry.

There are a few barrels up there and go to the one to the far right at the end of the lorry.

If you crouch down you can go inside it and no-one from outside can see you!