First Allies have to escort the tank to the main gate. It's about a 2 minutes way where Allies have also to destroy a tank barrier. If the tank blew up the main gate Allies are able to build a command post. Now Allies have to destroy the depot gate either with dynamite or with the train which can be driven into the gate. In the depot there's the ignitor. It has to be carried along the white line to the ignition area next to the depot. The ignition can only be done by an engineer and destroys the tanks in the depot. If so Allies won.
The sense of building a shelf between two windows is narrowed only for building the german command post.