A Twist of Sand (1968)

Synopsis
A former World War II submarine captain and his friend turn to smuggling when a former crew member lays out a plan to retrieve some hidden diamonds. Geoffrey (Richard Johnson) and his sidekick David (Roy Dotrice) listen to Riker (Jeremy Kemp) as he tells of the hidden treasure near the Skeleton Coast of Africa. Julie (Honor Blackman) is the passenger whose late husband supposedly hid the diamonds. With a dim-witted German named Johann (Peter Vaughan) as their guide, the crew battle fierce storms and underwater danger as they make the treacherous trek to collect the missing diamonds in this action adventure. ~ Dan Pavlides, All Movie Guide