Below the Sea (1933)

After a German U-boat is sunk near the end of World War I, it's captain, the only living member of the crew 15 years later, plots to retrieve the gold bullion that went down with the boat. He enlists the financial help of a woman who owns a waterfront dive, and a world-renowned undersea diver, but when the ship the woman bankrolls sinks, the two men sign on to an expedition bankrolled by another woman -- this time with scientific knowledge being her motive. They plan to use the expedition's equipment to dive to the wreck and bring up the gold.