What military vehicle did Leonardo da Vinci sketch as a cone-shaped armored platform moved by internal cranks?

Leonardo da Vinci sketched an armored fighting vehicle as a cone-shaped platform moved by internal cranks.

The design, created around 1487–1489, has a broad conical shell covered with metal plates and fitted with multiple guns around its lower edge. Inside, several operators would turn cranks connected to wheels, theoretically moving the vehicle across the battlefield while protecting its crew. Leonardo may have intended the design to impress Ludovico Sforza, the ruler of Milan, as part of a proposal for military engineering services.

The vehicle is sometimes called Leonardo’s tank, but that modern label can obscure its limitations. The surviving drawing appears to contain a gear arrangement that would make the wheels turn in opposite directions, so the machine may have been deliberately flawed or simply impractical. It was never built by Leonardo and did not lead directly to the tracked tanks used in the 20th century.