Battle Tanks were weapons of war manufactured by one of the armies in The Final War. Their rounded, green bodies were made of reinforced metal and the technology inside allowed them to fire powerful laser blasts from their cannons instead of artillery shells.
Apparently, they could be operated by monsters as well, because some are seen in the anime series bearing the symbol of the Baddies under the control of Moo's rebel forces.
More than likely, this technology was the basis for the creation of the original Tanklon.