The film presents an unsettling portrayal of life aboard a British submarine during wartime, offering a glimpse into the dangers encountered by those serving in the Royal Navy. John Mills portrays Captain "Armstrong," leading his crew on what seems like a standard patrol until their vessel becomes entangled in a minefield cable. The abrupt halt and reversal of engines prove ineffective, sending them to the seabed. Miraculously, the submarine remains largely intact and isn't in extremely deep water, fostering initial hope for rescue. Assistance arrives relatively quickly, enabling the first four of the twelve survivors to utilize their emergency equipment and ascend to the surface. As the air supply diminishes, a palpable feeling of confinement emerges; First Officer "Manson" (Nigel Patrick) falls ill, and "Snipe" (Richard Attenborough) reveals he enlisted for the additional compensation and is struggling with claustrophobia. With four men already gone, another group of four prepares to escape—but complications arise. The explosion’s damage has depleted the available emergency kits, necessitating a random selection process that heightens the suspense as those left behind must await the submarine's salvage, which hinges on favorable weather conditions above. The narrative unfolds effectively, with Mills demonstrating good chemistry with Patrick and James Hayter, who delivers a memorable performance as the cook and general assistant "Higgins." Attenborough convincingly conveys a sense of panic regarding his confinement within the metal hull and the subsequent remorse over his initial motivations. The script blends moments of dark humor with the escalating danger, and director Roy Baker maintains a brisk tempo throughout this surprisingly powerful story.

Source on TMDB