Cousteau and the Undersea Research Group tried out the research submarine, Hull Number One, they had been developing for 5 years in 1958. They lowered Hull Number One that was unmanned to 2000 feet at the end of a cable. When it was coming up and 100 feet from the surface, the cable broke and Hull Number One plummeted 3300 feet to the seabed. Thereafter, they started work on Hull Number Two.

Hull Number Two, renamed La souscoupe Plongeante – The Diving Saucer was tested in 80 feet of water on the  Caribbean continental shelf off Puerto Rico. After many successful dives, Cousteau and Falco aboard the diving saucer descended to 360 feet till they started sinking as there was a short circuit. They released the ascent ballast and they rose up to the surface. 2 months later, The diving saucer successfully brought Cousteau and Falco to 1,000 feet and safely returned to the surface. In the next year, the diving saucer carried geologists and biologists and gathered samples of rocks and new sea creatures with its hydraulic claw.