Leonardo da Vinci proposed a diving bell as an underwater enclosure for divers.
A diving bell is an open-bottomed chamber lowered into water with air trapped inside. Leonardo studied underwater devices in the late 15th and early 16th centuries and described equipment that could provide a diver with air while submerged. His work belongs to a much longer history of diving bells, whose basic principle was known before his time.
The air space inside a bell shrinks as water pressure increases with depth. This limits how deeply and how long a person can remain inside unless fresh air is supplied. Leonardo's proposals addressed underwater work and military use, but they were not modern, independently tested diving systems.
A diving bell is different from Leonardo's diving suit. The bell is a chamber surrounding the diver or divers, whereas a suit is worn on the body and uses tubes or another breathing arrangement. Both concepts show Leonardo applying pressure and buoyancy ideas to naval engineering.