In R. Frank Busby's book Manned Submersibles, it is stated on page 53 that the Deepstar 4000 "conducted some 500 dives from June 1966 through June 1968".
In R. Frank Busby's book Manned Submersibles, on page 53, it is mentioned that the Deepstar 4000 "performed some 500 dives from June 1966 to June 1968".