Leonardo da Vinci described a submarine as a secretive underwater machine for naval warfare.
In a note commonly associated with his studies of watercraft, Leonardo referred to a vessel that could travel underwater and attack enemy ships. He is also said to have withheld complete details because he feared that such a machine could be used for sinking vessels and killing crews. The surviving evidence is limited, and no complete working Leonardo submarine design is known.
This idea differs from Leonardo’s diving equipment, which was intended to help a person operate underwater. A submarine is a vessel that carries people or equipment beneath the surface, while a diving bell remains connected to the surface or depends on an external support system.
Leonardo’s proposal came centuries before practical submarines. Later submarine development required reliable control of buoyancy, pressure, propulsion, steering, and breathable air. His note is therefore best understood as an early conceptual contribution to underwater navigation, not proof of a functioning Renaissance submarine.