Leonardo da Vinci himself said that because it was a lethal weapon, it must not fall into enemy hands. This may be another reason why instead of drawing the final project, he drew it disassembled and in a way that makes it difficult to understand.

A boat with sails has a part that is submerged in the water and invisible to enemies. The pilot used a passage to get into the lower part undercover: the Mechanical Submarine. A pulley and rope system lowers the submarine, which can unhook itself underwater and proceed invisibly towards the enemy. The submarine has two air chambers, which can be used for steering and for air needed by the pilot, who has a mouthpiece. Steering underwater is done by means of a mechanical system.