What armored vehicle did Leonardo da Vinci design with angled plates and internal wheels?

Leonardo da Vinci's armored tank was a conical, turtle-shaped fighting vehicle driven by internal cranks and protected by sloped armor. His drawing dates from about 1487–1489 and shows a circular platform covered with metal plates, with light cannons projecting around the perimeter.

The sloped shell could deflect incoming projectiles, while several men inside would turn cranks connected to wheels. Leonardo presented the vehicle as a battlefield machine, probably for the patron Ludovico Sforza. The design has no evidence of being built or used in a fifteenth-century battle.

A famous problem is that the gears in the surviving sketch would make the vehicle move backward if built exactly as drawn. Some historians think this was deliberate concealment or simply an error. Modern replicas add corrected gearing and demonstrate that the concept can move, but they are reconstructions, not surviving Renaissance tanks.