there was quite a modern, small tank they used in a film at Pinewood Studios that was stored in the same farm that we kept fencing materials when i was much younger. Two of us kids knew that the key was hidden under the skirt, was just like a car key. You had to open the hatch with one key and use another in the ignition. We used to hide in there so no one would catch us smoking, it became quite hard to breath in there after a few minutes. They never left it with a battery or any fuel in but we did see them driving it when they took it away.