Almost all the tanks in this movie are 1:16 highly detailed models, combined with outdoor footage. However, for the scenes inside the tank, a full scale model of tank internals was built. Also, one tank was a 1:1 size model, built for the movie from scratch.
To get shots of model tanks to look realistic, they were shot at x4 speed. The camera was mounted on a KUKA robotic arm (such as used at assembly lines), so it could reproduce the motion of outdoors camera.