Cracked, in its own inimitable way, is featuring this look at "7 WTF Military weapons". Being an armchair student of all things various armies have attempted over, well, all of detectable history I suppose, I'm not at all surprised things like this got built. I'm actually rather surprised that any of them survived.
Between WWI and WWII, there were attempts to build gliding tanks. Like many "flying car" designs, it amounted to clamping wings on a tank. Wikipedia:
http://en.wikipedia.org/wiki/Winged_tank
One Soviet design put a tail on the muzzle of the barrel. You steered by rotating the turret and elevating the gun. That was the concept.