U-Boat Prisoner

Bruce Bennett is a merchant mariner whose ship is torpedoed after a German spy aboard sent the coordinates to the Nazty Nazis. Bennett spots him going overboard, and takes his place and documents, convincing Gestapo man John Wengraf he is the spy. Wengraf assigns him to spy on prisoners they're taking back to the Fatherland, brilliant scientists they hope will turn coat to save their families, if not themselves. Meanwhile, up above, a crippled ship and its naval convoy decide to play cat-and-mouse with the sub's captain, Erik Rolf.

The sub-vs-destroyer sequences are ok, and Bennett plays the sort of guy who thinks with his fists, and that's enough to come out on top after a few speeches. Shot on a couple of sets, it's clearly B material directed by Lew Landers with uncredited assistance from Bud Boetticher.