At the start of this map, it's better to not move your squads just yet (those underneath the castle from the southeast to the southwest). You will not only run into a minefield and entrenched opposition, but this will also trigger the enemy/AI to man the tanks that are stationed right above the castle. So instead, wait for your matildas to arrive in the east and order them to go north to get behind the castle. When ready, attack the northwestern gate and even the northeastern gate of the fort. However, at the latter, beware for some enemy/AI troops coming from the northeast.

The enemy/AI artillery will be pretty hurtful; it is located east and south within the fort. Try to silence these as quickly as possible with your own artillery. Doing so with make the mission much easier.

Once the fort is under your complete control, the entrenched enemy units will surrender. If at this point, the objective remains unfinished, look for some enemy/AI units underneath the fort that have not surrendered maybe.