Gray Lady Down

Gray Lady Down is a 1978 disaster film by Universal Studios starring Charlton Heston, David Carradine, Stacy Keach, Ned Beatty, Ronny Cox and Rosemary Forsyth, and includes the feature film debut of Christopher Reeve. It is based on David Lavallees book Event 1000.

A small experimental submersible, Snark, is brought in to assist with the rescue. Snark is very capable, but run by a nonconformist U.S. Navy officer misfit, Captain Gates Carradine. The tiny submersible is the only hope for a rescue. Ultimately, the surviving members of the crew are rescued by the DSRV, thanks to Gates sacrificing himself by using the Snark to jam the Neptune in place as another gravity slide begins while the rescue is taking place. Moments later the gravity slide forces both the Neptune and the Snark from the ledge and to the bottom of the sea.Ronny Cox plays Neptune s executive officer, scheduled to take over command from Charlton Heston s character Ned Beatty plays Snark s second crewman and Christopher Reeve appears in his first film role. ........

Source: Wikipedia