Audio problem: When the U-boat captain is called onto deck,he orders his machine gunner to fire at the sailors who are rowing towards them. As soon as he fires the ammo belt gets used up straight away, however the sound of the gun carries on for a short while longer. (00:27:50)
Factual error: It takes a whole of two minutes from the discovery of the boarding party and the cry "Alarm" till the first Americans even enter the command central of U-571, and another almost 90 seconds till they secure the radio room. German subs were under strict orders to destroy all secret material the instant they had reason to believe a boarding was probable. To that end, all code books were printed in water-soluble inks on water-soluble paper, and even the electrical connections inside the rotors of the enigma machine were seawater-soluble. (Admittedly the latter was more with the idea of enemies salvaging sunk boats in mind, and I have no information on how fast that decay would have happened) All it would have taken is to lift up one of the floor plates and drop the stuff into the bilge below. And yes, since German subs of the era didn't have answering machines, the radio room would be manned around the clock. For that reason, boarding actions of that sort had to be above all lightning-fast. Dramatic as the fight scene is, in reality it would have ensured that the boarding party came away empty-handed. (00:38:30 - 00:41:45)
Factual error: When the American crew storms the U-571 and reaches the aft compartment, where the last Germans are gathered, we can see a row of bunks on each side of the chamber. The VIIC type has no crew acommodation in this place; the last compartment houses just the electric motors and some pumps and auxiliary machinery, as well as the breach of the aft torpedo tube. (00:43:30)
Continuity mistake: When the German in the bunk goes to shoot Matthew McConaughey, the man fires but the bullet doesn't hit the wall, only about 2 feet away, for a much longer time than it would have really taken. Also, when the American soldiers pass by the spot a few minutes later where the bullet hit (when they are looking at the dead German's ring) the bullet hole has suddenly disappeared. (00:43:40)
Other mistake: There is a scene where Eddie, the mess steward, is taunting the German prisoners while writing numbers on their chests. Watch his writing hand as he's working on 11. He makes an awful lot of strokes, including several horizontal ones. You can see from the next guy, 12, that Eddie's ones are just simple vertical lines, so there's no reason for him to have spent so much time writing on 11's chest. Except that it gave him time to say his whole line. (00:45:40)
Continuity mistake: When the S-33 is torpedoed, the boarding party members (including Tank) stand motionless, staring at the destruction in horror. Then Tank shouts "The scuttling charge!" and hurries towards the aft hatch to disable the explosives. Five seconds later, as the Chief throws a rope to Tyler, Tank can be seen standing motionless behind him, still staring at the destruction in horror. (00:48:30)
Deliberate mistake: When the Americans are in the U-571 battling the resupply sub, Tank gets the engines running and starts the sub moving forward. There is an exterior shot of the sub's propellers, with the port prop turning counterclockwise and the starboard prop turning clockwise. Then Tyler wants to turn right to heading 010, and he orders "Starboard back full", which should reverse the direction of the starboard propeller to help turn the sub. Two exterior shots later, however, the props are shown still turning exactly the same way they were before Tank reversed the starboard engine. (00:52:00 - 00:53:35)
Factual error: When the Americans are initially scrambling to figure out how the German submarine works, Rabbit opens a torpedo breech door, closes it and reports to Tyler "We have four fish, tubes are flooded." They are obviously not all flooded, otherwise Rabbit would just have flooded the compartment by opening the breech. (00:53:12)
Factual error: When Rabbit first checks the German sub's torpedo tubes, we catch a glimpse of the torpedo loaded in the tube, its propulsion screws visible. It is loaded incorrectly and missing the piston-type device put in behind the torpedo which pushes the torpedo out via compressed air. This torpedo wouldn't go anywhere when fired. (00:53:12)
Factual error: Shortly after the crew of the S33 are forced to take to the U571 and destroy the German Supply Submarine Tyler announces that they will try to sail to Greenland or Land's End (England). From their mid-Atlantic position they would, therefore, need to sail east. In the next scene the submarine is seen on the surface sailing from left to right across the screen with the sun on the other side of them. Since from the North Atlantic the sun would always be to the south this must mean they are sailing west, away from Greenland and England and towards the United States. (00:57:05 - 00:59:25)
Audio problem: When they spot the long range plane circling the U boat Mazzola starts yelling saying, "Do something Rabbit." A quick shot later you notice that he is still talking but his mouth is not moving. (01:06:00)
Continuity mistake: When Mazzola is shot in the engine room he takes down the German, first he has hold of the German by the neck, then the collar, then the neck, then the collar again. (01:08:35)
Continuity mistake: After the German captain has attacked Tank and handcuffed him to the crane, the pattern of blood on Tank's face changes at least twice. First, he has two channels of blood running down the left side of his face under his nose and on his chin, and no blood on his lips or the right side of his face. Then, when Eddie and Tyler arrive, there is blood smeared all over Tank's nose and lips. Finally, after Tyler takes the cuff off and is yelling at Tank, all of a sudden there is a line of blood from Tank's nose across his cheek to his right ear. (01:09:05)
Continuity mistake: When Tyler is unhandcuffing Tank and Mazzola's body is lying beside him, in the long shot of the scene, it looks like Tank and Mazzola are a few feet away from each other. But in the overhead shot, they're right beside each other. (01:09:20)
Continuity mistake: Just after Mazzola's been killed, Tyler unlocks the handcuffs from Tank. The handcuff starts swinging as soon as Tank pulls his hand free, but in the next shot it's stopped moving. (01:09:42)
Continuity mistake: Just after shooting the radio room on the German destroyer, U-571 submerges so quickly that the sailors do not manage to plug the gun. After a few moments when the boat goes from 180 to 200 meters there is a short shot from the above when we can clearly see that the gun is perfectly plugged. (01:13:30)
Factual error: The film is set during the war and there is a Toyota forklift driving around in one of the dock scenes.... (01:19:45)
Continuity mistake: When the U-571 goes to 200m, it springs a bunch of leaks and everybody gets soaked. Then, there is a shot looking past Tank's left shoulder at Tyler and the chief talking. In this shot, Tank's shoulder is completely dry. The camera angle changes and then changes back, and in the next shot at this same angle Tank's coat is now dripping with water. (01:35:50)
Factual error: In the last battle scene when you see shots of the German destroyer through the periscope the last one shot before it's blown up is really bad angling. The ship is far away but in the scope it's very close and the periscope (in order to get that camera angle) is 100 ft in the air.
Character mistake: After accurately depth charging U-571, the German destroyer crew suddenly turns out to be almost comically and unrealistically incompetent at the end of the movie. Not only do they barely hit U-571 with their guns, but they also can't keep up with the sub. But even with both submarine diesel engines running flank speed (of which U-571 only has one badly damaged engine operational), a common WWII destroyer would easily be twice as fast as a Type VII U-boat. The destroyer could swiftly close the distance and could either ram U-571 or cross the sub's wake to bring all its weapons to bear and make it more difficult to get hit by the sub. Of course the destroyer doesn't do that but stays perfectly in U-571's wake for an easy kill shot from its stern tube. In reality, it was considered an incredible feat to sink a destroyer with a torpedo, since they were agile at full speed, could easily dodge torpedoes and had shallow draft. This destroyer crew however, seems actively trying to get killed.
Answer: The scars you see on Tank's face are fake, pure makeup. They wanted the character to have a gritty look.