A distinguished cast star in this dramatic World War II story that has the true claustrophobic feeling of being submerged, but the documentary style and stiff-upper-lipped stereotypes diminish the overall pace of the film. Based on a true-life incident, the Tirpitz was subsequently sunk by a bomb especially designed for the job by inventor Sir Barnes Wallis. The story charts Navy commander Fraser's (John Mills) attempt to sink the German pocket battleship Tirpitz in a Norwegian fjord. With the RAF having failed to sink her on numerous bombing missions, Fraser must win the confidence of Admiral Ryder (James Robertson-Justice) to carry out an attack on the German battleship using midget submarines. After rigorous training, Fraser initially develops an experimental submarine chariot that will effectively become a human torpedo, and after overseeing the planting of dummy explosives on the hull of a British battleship guarded by nets, he wins the approval of his superiors to attempt the hazardous mission. The initial attempt involves a mini-sub attached to the hull of a trawler to avoid German detection, but fails when the men are caught in neutral territory and sent back from Sweden to Scotland. A second mission is attempted, this time with three X-Type mini-subs towed across the North Sea by submarines. Once near their destination, the mini-subs make their way unaccompanied anxiously through the Norwegian fjord toward the anchorage of the Tirpitz, avoiding booms and nets along the way. The surviving submariners deploy their explosive cargo beneath the Tirpitz’s hull before bailing out and surrendering to the Germans.