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 work "Manned Submersibles", it is stated on page 53 that the Deepstar 4000 undertook around 500 dives from June 1966 to June 1968.