I just played a game of Fao Fortress, we were getting beaten and had the dubious fortune to get the Behemoth. I spawned on at found myself on the big gun at the back.
The driver spent the remainder of the game back near our own spawn with the ship pointing directly at the land. The rear gun only points towards the rear, so was no use to anybody.
So, Battleship drivers, please make an effort to position the ship so that all the guns get to be used. If you're going to give up on winning the game and just want to farm some cheap kills, at least let the rest of us have some fun too.