What defensive feature did Leonardo da Vinci add around some military machines?

Leonardo da Vinci added sloped armor to some military-machine designs, especially his armored fighting vehicle. The vehicle’s outer shell used angled plates rather than a simple vertical wall.

Sloping armor can improve protection by making incoming projectiles strike at an angle. That can increase the effective thickness of the material and encourage a projectile to deflect instead of penetrating directly. Leonardo’s drawing therefore contains a defensive principle that later became important in armored vehicle engineering.

The design should not be treated as a fully tested tank prototype. Leonardo’s vehicle also had a mechanical problem: the apparent arrangement of its gears would make the wheels turn in opposite directions. Some historians have suggested that this may have been deliberate, perhaps to prevent unauthorized construction, while others regard it as an error. Whatever the reason, the surviving design clearly shows Leonardo combining armor, mobility, and mounted guns in a single military machine.