I believe the film you are looking for is titled "Submarine Base" (1943). Here is the plot summary from IMDB. Hope this is the one you were looking for.

Ship engineer Jim Taggert is rescued from a torpedoed tramp steamer by Joe Morgan, an American gangster that found New York too hot for him, and has become a fisherman operating from an out-of-the-way island off of the coast of South America. Morgan makes his headquarters at the Halfway House run by the parents of Maria Styx as a bar and dance resort catering to the planters and traders of the island. Taggert finds himself practically a prisoner along with a group of American girls acting as entertainers at the resort. Taggert shadows Morgan in his activities in a remote cove and finds that Morgan is supplying German U-boat commanders with torpedoes, but does not know that Morgan has rigged the torpedoes with clock devices that explode when at sea and sinks the U-boats.