Abstract: A self-propelled submersible vehicle which comprises a hull and a cockpit defined within the hull, a transparent dome on the top of the hull formed with the cockpit and enclosure walls defining the cockpit within the hull. The cockpit is open ended at the bottom thereof, and the hull is non-watertight. Compressed air tanks are provided in the hull, and these tanks communicate with a regulator valve which provides a constant flow of air into the cockpit forming an air bubble providing a breathable section of the cockpit for the passengers. An air exhaust device is incorporated with the regulator valve assembly for controlling the volume of the air bubble within the cockpit in response to the water level within the cockpit.