Long time ago I saw an anime and I forgot its title. The story revolves around an experimental ai tank (nothing fancy, kind of like a dark green abrams as I remember), and a girl who gets into it and after that the tank goes out of control. Later it was found out that it wants to protect the girl. The story ends that the tank fires its last shell, which cause of a program written for that, causes it to self destruct. Thats all I could remember and that I really liked it, anyone has any ideas what the title could be?