In the midst of World War II, a critical mission is embarked upon by an American submarine crew. Their objective is of immense strategic importance: to seize a German Enigma machine, a device essential for decrypting Nazi Germany's coded communications. Successfully capturing this machine could turn the tide of the war by allowing the Allies to intercept and decipher German messages, giving them a much-needed advantage. The crew, led by a determined but inexperienced captain, must pose as Nazis and infiltrate a German U-boat to execute their mission. However, they quickly find themselves in treacherous waters, both literally and figuratively, as their plan encounters unforeseen challenges.

The operation takes a perilous turn when the crew’s own submarine is destroyed, leaving them stranded aboard the enemy U-boat they have just commandeered. With no other options, they must navigate the captured vessel through hostile waters, evading detection and attack by the German Navy. The team's cohesion and resolve are tested to their limits as they encounter the harsh realities of war and the grave risks of their undertaking. They must rely on their wits, courage, and the limited resources available on the German sub to complete their mission and attempt a perilous journey back to friendly territory, all while maintaining the facade of being a German crew to avoid discovery and capture.