From Depths So Deep — George W.J. Laidlaw

The bottom of the sea hold many remains of man's effort to sail the oceans. Michael Stone's life as a US diver is ruined when he risks his life to rescue two men in a bathyscaph trapped on a sea plateau where they are working on two iron age wrecks. That dive nearly killed Stone but he also finds a mystery about a German U-boat-443 that brings the ghosts of the Second World War too close to home. Both the U-boat and the suicide of his boss brings him to face death at its very deepest depth. He is forced to dive again because the lady he loves will be killed if he doesn't recover diamonds that was lost on board a tramp steamer destroyed by the Israeli intelligence because it was being used to transport arms to the Palestinians.