There's two objectives in this map. The first is to defend the fort and the second to go get some reinforcements in the east of the map. Do not let the enemy/AI surprise you; their main attack will come from the back (northwest and northeast). Therefor, you will need to act very swift here as most of the equipment is still unmanned.

As soon as your artillery is manned, immediately aim it south and try to take out the enemy/AI artillery before it starts shelling you. At the same time, urge some of your troops to defend the northwest gate and northeast gate. Prepare for a heavy attack and don't let the enemy/AI capture your flag!