Despite the efforts of the crew aboard U-571 to deceive and fend off the German destroyer that is on to them -which include tossing debris and the corpse of Mazzola (Erik Palladino), to make believe the submarine is destroyed-, the destroyer drops depth charges that blow off and cause further shockwave damage. Then, Wentz (Jack Noseworthy) catches wind of a weird tapping sequence on the sonar that turns out to be a message in Morse code ("I am U-571. Destroy me!"); they realize that Wassner (Thomas Krestchmann), the enemy crew member they had kept captive, despite being shackled, had been warning his own comrades all along. Hirsch (Jake Weber) comes at him with a wrench and apparently beats him to death -his fate is left unknown.
To elude the destroyer, U-571 has to go several meters under, which causes the water pressure to render it just about inoperable. As they start to sink, Tyler (Matthew McConaughey) orders to ascend all the way to the surface, to avoid death. At the same time, he orders Trigger (Tom Guiry) to dive into the bilge -now fully underwater-, to adjust the valve that would allow them to use the last functioning torpedo. Trigger struggles to adjust the valve, but spots another leak that he can't get to without leaving his breathing tank behind. Tyler goads him to fight and get to it "because he is everybody's last chance".
Meanwhile, the destroyer pursues and openly fires at U-571, which is unable to fight back due to the issue with the torpedo and is slowly flooding. One of the explosions traps Trigger away from his hose; seeing he is doomed to drown, he, at least, manages to fix the last valve. This gives the crew one final chance and they fire the torpedo, successfully blowing up and sinking the destroyer. Tank (Dave Power) reports the demise of Trigger, which Tyler commends as a brave sacrifice.
Once it is acknowledged that U-571 doesn't have much time left before inevitably sinking for good, the survivors abandon it, in possession of the Enigma machine. After a while floating adrift on a lifeboat, they are spotted and rescued by a military flying boat. The movie ends while title cards inform of all the fights in which other German U-boats suffered similar defeats in the Battle of the Atlantic.