What type of warship did Leonardo da Vinci propose with two layers of hull for better protection?

Leonardo da Vinci proposed a double-hulled ship with two layers of hull for greater protection.

The concept placed an additional outer layer around the ship’s main hull. Leonardo’s military reasoning was that a second shell could help protect the vessel from impact and weapons fire. The design belongs to his broader studies of naval warfare, ship construction, and methods of improving a vessel’s survivability.

A double-hulled ship should not be confused with a submarine. Leonardo also produced sketches connected with underwater vessels, but the double-hull proposal described here is a surface warship concept rather than a craft intended to remain submerged. It is likewise not simply a catamaran, whose two hulls are normally separate and parallel.

As with many of Leonardo’s military inventions, the proposal survives primarily through drawings and notes rather than evidence of successful construction or deployment.