SEALAB III used a refurbished SEALAB II habitat, but was placed in water three times as deep. Five teams of nine divers were scheduled to spend 12 days each in the habitat, testing new salvage techniques and conducting oceanographic and fishery studies. Preparations for such a deep dive were extensive. In addition to many biomedical studies, work-up dives were conducted at the U.S. Navy Experimental Diving Unit at the Washington D.C. Navy Yard. These “dives” were not done in the open sea, but in a special hyperbaric chamber that could recreate the pressures at depths as great as 1,025 fsw (312 m).
On February 15, 1969, SEALAB III was lowered to 610 fsw (185 m), off San Clemente Island, California.