Tanks drive just as easily backwards as they do forwards. They're like a locomotive that way. They're just as happy to be thrown into reverse and just go. This fact really came in handy when the British were looking for a way to get their 17-pdr anti-tank gun some more speed and mobility on the battlefield. It was a very potent gun, but a pain in the britches to carry around. Thankfully, they had a whole bunch of Valentine tanks sitting around that, well, they weren't top-of-the-line anymore. So they had to do something with them.
Unfortunately, the gun was too cumbersome to put in a turret. Also, the mounting wasn't really right to have the large gun pointing forward off the chassis. So... just turn the chassis around. Boom! Self-Propelled Anti-Tank Gun with a nice, low profile to it that was great for ambushing the enemy. Not only were they used extensively in Europe during WWII, but also by the Egyptian Army during the Suez Canal Crisis in 1956.
Now you can add it to your Bolt Action armies. Go and pick yourself up one from the Warlord Games webshop.
Oh, and "Do you want ants? Because that's how you get ants."
Because, you know, Archer.