Leonardo da Vinci designed an underwater breathing device in the form of a diving bell.
His notebooks include ideas for enabling a diver to remain below the surface while receiving air from above. A diving bell is a chamber open at the bottom that traps air as it is lowered into water. Water pressure compresses the air inside, but the trapped air can provide a temporary breathing space.
Leonardo’s underwater studies were connected to military and engineering problems, including the possibility of operating beneath enemy vessels. Some accounts associate his designs with a breathing tube and related underwater equipment, but the surviving drawings do not prove that Leonardo built and tested a complete practical system.
A diving bell is different from the flexible protective diving suit also associated with Leonardo. The bell is a chamber; the suit is worn by an individual.