This is a fairly routine and predictable World War 2 submarine action film.Second billed is James Robertson Justice but he barely appears for more than 5 minutes.A U boat is captured in tact with all its codes.No mention of enigma or ultra ,as this was before the ban on their mention had been lifted.A specialist naval officer,Judd,is made captain of the boat.His no 1 is Payne and their disagreements form much of the drama inside the sub.The crew is the usual motley collection including a vociferous Irish engineer.The sub is sent to the Bay of Biscay to rendezvous with a waiting wolf pack,so that it can radio back to the Admiralty the number of subs and their position.Its radio signals are detected and there follows a duel between Judd and a German sub in the depths.Whilst the sub escapes the enemy it is eventually sunk by friendly fire with the crew escaping.One final thought ,once the GHermans realised that the British had captured their sub,they would realise that their codes had been compromised and change them.So sending the sub to locate the U boat pack would be counterproductive.