World War II. The Allies torpedoed the German submarine U-571, which was carrying the secret Enigma device. The sub remained afloat awaiting assistance, and the Americans decided to seize Enigma, sending their submarine S-33 to U-571, disguised as a German vessel. The operation went perfectly, and the American sailors managed to infiltrate the enemy submarine and capture the Enigma, but a German cruiser suddenly appeared and sank the S-33, leaving the sailors with only one way to escape: the partially operational U-571.