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 metres (1,300 ft).

Denise's 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.

If the craft is within 100 metres (330 ft) of the surface, the crew can abandon it via the top hatch, provided they are equipped with emergency breathing apparatus.