Forgot the name of an anime?

Okay, the details are really vague. What I remember is that it was a village of some sort that was attacked and one guy and a girl, maybe, retaliated with some old weapons. I think it looked like a tank but like I said the details are vague. I think the guy joined the military and he was a commander of a group. The group conducted a task that involved an ambush or attack near or on a lake or bady of water. However, this second part might be a different anime and I am confusing the details of both.