SP-350 Denise

The SP-350 Denise, famous as the "Diving saucer" (Soucoupe plongeante), is a small submarine designed to hold two people, and is capable of exploring depths of up to 400 m. It was invented by Jacques-Yves Cousteau and engineer Jean Mollard at the French Centre for Undersea Research.

Its propulsion consists of steerable, electrically powered water jets, allowing it to navigate in all directions, as well as turn about its vertical axis. The crew members enter the craft through a hatch on the top of the hull and lie prone side-by-side on mattresses to operate it, watching their surroundings through tilted portholes that let them come within a few centimeters of their subject. Electric lamps are fitted for night diving and to provide illumination for photography at extreme working depths. An electrically operated manipulator arm can be fitted at the front of the craft so that objects can be picked up and examined through the portholes.

The steel pressure hull, nearly circular in plan form, is 2 m in diameter and 1.43 m high, able to resist a pressure of more than 90 kg/cm2, equivalent to a depth of nearly 900 m, although dives never exceed 300 m for safety.

Despite having positive buoyancy, Denise is weighted to negative buoyancy with ballast weights that can be jettisoned in an emergency. To correct the attitude of the hull, the pilot can shift a liquid mercury ballast mass.

If the craft is within 100 m of the surface, the crew can abandon it via the top hatch, provided they are equipped with emergency breathing apparatus.

Launching and recovery is accomplished with the assistance of a shipboard crane.