Plot

A German submarine is boarded by disguised American submariners trying to capture their Enigma cipher machine.

In the midst of World War II, the battle below the seas rages. The Nazis have the upper edge as the Allies are unable to crack their war codes. That is, until a wrecked U-boat sends out an SOS signal, and the Allies realize this is their chance to seize the 'enigma coding machine'. But masquerading as Nazis and taking over the U-boat is the smallest of their problems. The action really begins when they get stranded on the U-boat.—Filmtwob <webmaster@filmfreak.co.za>

During World War II, the Allies were having trouble against the German Navy especially their U-Boats because of their highly sophisticated cipher machines. When a German U-Boat is damaged and is waiting for assistance, the Americans decide that this is an opportunity for them to get the machine. So they have one of their subs made up to look like a German, and plan to pretend to be the ship sent to assist them and take control of the U-Boat and take the machine and destroy the sub so that the Germans will not know that they have the machine. And everything went according to plan; they got the machine and transferred the crew to their sub and were about to leave when out of nowhere they're hit by a torpedo from the German relief sub. The members of the crew who were not on board the sub, proceed to board the German U-Boat and try to make it back. Now the senior officer is the sub's XO who's eager to be in command but his commander had told him earlier that he felt he was not ready because he might not be ready to make tough decisions. And now he has to, if he and the survivors are to survive.—rcs0411@yahoo.com

In the battle front of espionage and code cracking of World War II, there remains but one task on the Allied agenda: the capture of a German "Enigma" machine which will allow the Allied naval forces to locate and track submerged German U-Boat submarines. When one such German vessel breaks down after a battle with British forces, a secret mission is dispatched to take over the U-Boat by commando American forces and retrieve an Enigma machine intact. The raid goes well, at first, yet following the destruction of the American mothership and the arrival of reenforcement German ships, the Americans trapped on the U-Boat must use their training and wits to pilot U-571 in order to save their lives.—Anthony Hughes <husnock31@hotmail.com>

The film begins with a summary on how the Allies are struggling to stop U-boats from sinking their freighters. The scene transfers to U-571, which torpedoes and sinks a freighter. The crew is happy with the kill but seconds later the sonar man reports to have detected high speed screws. The Captain turns the periscope to sight a destroyer moving in, forcing U-571 to dive.

The destroyer drops depth charges; unfortunately for the submarine, the depth charging snaps a fuel line which ignites while the engineers attempt to patch it, setting them all on fire. Due to the amount of damage sustained, the Captain orders U-571 to resurface.

The Captain learns from his Chief who extinguished the fire in the engine room that their batteries are practically flat, both diesel engines are inoperable and all of their engineering crew are dead. After passing word to conserve electricity, he has his radioman send an Enigma-encoded SOS to Berlin for aid.

Meanwhile, the crew of the United States Navy submarine S-33 are celebrating the wedding of Crewman Larson and leave for 48 hours. During the party, Lt. Andrew Tyler enters looking solemn, having been denied his own command. After complaining to Lt. Commander Dahlgren, he is rebuffed and upset to learn that Dahlgren voted against him receiving the promotion. While talking to Chief Henry Klough, Military Police suddenly arrive to announce the end of their shore leave for a secret mission.

All the men arrive at the base to find their boat, the S-33, being modified to resemble a German U-boat. The crewmen are given German uniforms to wear as well. Hirsch, a Naval Intelligence officer who is fluent in German, orders Tyler to locate Radioman Wentz, who is fluent in German due to his immigrant parents.

At the same time, a Marine named Coonan arrives in a convoy loaded with high explosives. After the S-33 sails, Hirsch explains that the Allies intercepted the disabled U-571's SOS. They are going to masquerade as the resupply ship U-571 called for, board the ship, capture her Enigma coding device and then scuttle the U-571.

Tyler is skeptical about the scheme working but goes along. Wentz privately asks Tyler to not tell the rest of the crew that his parents are German. Back on U-571, attempted repairs fail and the Captain is alerted that survivors from the merchant ship he sank have been spotted on a lifeboat asking for asylum. He orders his men to shoot them, as their orders are not to spare any survivors. His men reluctantly do so.

During a storm, the S-33 comes across U-571 and sends the boarding party over, led by Coonan. Hirsch temporarily freezes and Wentz is forced to speak German in front of his friends in order for the group to retain their cover until their rafts are tied up.

At first, the Germans openly welcome the S-33, but when a midshipman looks through his binoculars, he immediately identifies the weapons as American. He alerts the rest of the Germans and they exchange fire with the S-33 crewmen. The Americans are able to take the boat by force, capture the Enigma and begin rounding up the prisoners, including the Captain. As the prisoners are transferred between ships and the scuttling charges are laid, Dahlgren, standing on the upper deck of the S-33, notices the sound of a detonation. He turns around in horror to see a streak coming towards the S-33 underwater.

The ship is torpedoed and sunk by the real German resupply sub. CO Dahlgren, wounded in the water, orders his men on the captured U-boat to submerge and save themselves. (This scene was based on an actual incident in World War II) Coonan, Larson and many others are lost, forcing Tyler to take command and dive the captured U-boat.

There is a desperate scramble to disarm the charges they placed. With only Hirsch and Wentz able to read German, after struggling with interpreting the controls they fire a salvo of torpedoes, destroying the enemy U-Boat, draining the last of the sub's batteries and spending all but the last torpedo, loaded in the malfunctioning aft torpedo tube. Surfacing, Tyler and his men search for survivors and find two: Eddie the cook from the S-33 and a German sailor claiming to be an electrician, but who is actually the Captain of U-571.

After repairing one of the diesel engines, thus restoring power and propulsion, Tyler decides to take the disabled submarine to England. Some of the men disagree with Tyler's decision and Tyler replies with "I don't know" to their questions. Chief Klough privately rebukes Tyler, saying "A Captain always knows what to do, whether he does or not." He also rebukes Mazzola in front of others for openly disagreeing with Tyler. They spot an aircraft and Mazzola tries to convince Rabbit to fire on the plane with the deck gun against Tyler's orders, which appears to be coming in for an attack, but is only scouting for a German destroyer named the Anschluss.

Tyler punches Mazzola for ignoring the Chain of Command and his stupidity. The captured German Captain breaks free, attacks Tank and kills Mazzola before being subdued. Unaware that the U-571 has been commandeered by Americans, the Anschluss sends over a small contingent to meet and greet with their German comrades. Right before boarders arrive, Tyler has Rabbit fire a shot from the deck gun right into the ship's radio tower, preventing the destroyer from reporting that the enigma code has been compromised and dives underneath her. The destroyer begins to drop depth charges to try to sink U-571.

Tyler plans to trick the destroyer into stopping by ejecting debris and Mazzola's corpse out of an empty torpedo tube, faking their own destruction. The younger men balk at using their crewman's body this way, but Tyler states that Mazzola is saving their lives. U-571 will then surface and hit the ship with their last torpedo.

The German destroyer continues dropping depth charges. U-571, hiding at great depth of below 200 meters, is damaged by the high-water pressure. In preventing the submarine from sinking, control of the main ballast tank is lost, and the ship ascends uncontrollably. Tyler orders Trigger to submerse himself in the bilge underwater to re-pressurize the torpedo tubes. During the ascent the German prisoner tries to warn the destroyer in Morse Code that they're not dead yet. Wentz translates the message in German, "I am U-571. Destroy me!" Enraged, Hirsch grabs a large wrench and kills the prisoner.

Trigger manages to close the air valve for the tubes, but a second leak and valve is unexpectedly revealed, both behind a wall of pipes; Trigger's arm can't reach, and his air hose is too short. When Tank reports this, Tyler rushes to the engine room himself. Tyler tells him that they need him to do this and orders him to get the job done. U-571 surfaces without a torpedo to fire. The destroyer fires on the ship, which runs using its diesel engine, but takes heavy damage from the destroyer's deck guns and starts to flood.

Trigger leaves behind the air hose and closes the second valve, but the damage causes pipes to collapse, trapping his leg and he drowns. The second the pressure is available, Tyler orders Tank to fire the final torpedo.

The German ship is destroyed; in front of everyone, Chief Klough tells Tyler that if he ever needs a Chief, he will gladly go to sea with him anytime. Tank reports Trigger's death while carrying out his order, but U-571 has taken severe damage and will not stay afloat for long. The crew abandons ship with the Enigma in tow and watches it sink, seemingly mourning both for their lost crew-mates and also for the German sub which ironically saved their lives. Floating aboard an inflatable lifeboat, they are eventually spotted by a US Navy seaplane.