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.
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 the boarding party are eating dinner on SS-33 before the raid, some of their spanking-new, freshly pressed Kriegsmarine utility uniforms (strange in itself) have breast eagles on the left chest instead of the right. I've never seen any German Wehrmacht uniform with an eagle on the left.
Factual error: The submarine gets buzzed by a single engine German fighter. They are somewhere between the US coast and Greenland. The Germans had no aircraft carriers nor bases in the area. Since it was not a float plane how did the fighter get there? It could not possibly have flown the several thousand miles from continental Europe.
Factual error: At the beginning of the film the German commander is shown directing an attack using the periscope in the control room. German U-boats had two periscopes: a 'sky' scope (the one in the control room) used exclusively for searching the area directly above the boat prior to surfacing, and the 'attack' periscope located in the conning tower (turm). There'd be no sense in the commander using the sky scope - the attack scope had an integrated firing switch, much more stable view, smaller outline over water and better magnification. (00:03:00)
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)
Factual error: In the ship yard after the party, one of the navy crew is working on a sub and he is using a yellow plastic handled grinder. All tools in this era were metal handled. He's also wearing tennis shoes. (00:13:15)
Factual error: The language the American soldier and the secret-service officer use is grammatically correct German, but the pronunciation is very bad. No born German would ever be fooled by it.
Factual error: The German supply U-boat couldn't have sunk the S-33 with a torpedo, as neither the Type XIV nor any other class of German supply sub was equipped with torpedoes (this would have meant less storage space for cargo).
Factual error: At the beginning of the film the depth charge attack is shown rupturing a diesel fuel line in the engine room, which showers the fuel DOWN on the crew stationed there. In fact the fuel lines ran UNDER the deck plates and so a broken line could not shower fuel in that manner. (00:05:55)
Factual error: The "German" airplane which spots the crew before the destroyer scene is actually a Fiat G59 - a post-war two-seat training development of the G55 Centauro fighter. It is powered by a Rolls Royce Merlin engine.
Factual error: When the marine commando shows the sailor his "luggage" (the boxes of explosives) to be loaded onto the submarine, some of the boxes have orange Explosive B placards. Those are Dept. of Transportation placards. The D.O.T. didn't exist until 1966 and the placards were not used until later than that. (00:19:55)
Factual error: Although the type of mission depicted in the movie did occur, it was not Americans that were known to do them. Canadian and British teams were specialized to do this mission.
Factual error: In reality, the planned boarding of the disabled sub would have been doomed to fail once the American and German subs met. Whenever German U-boats or ships met at sea, they were required to exchange a secret signal, usually consisting of a challenge-and-response using differently colored signal pistols. These signals changed daily and the Americans had no way of knowing this information.
Factual error: After the Americans have stormed the German sub, they find the Germans tried to destroy the Enigma code books by throwing them into the bilge water, which is just below the deckplates in the torpedo room. However, there was actually a lot of room for machinery and reserve torpedoes under the deckplates, which means that the torpedo room would have to be flooded by more than 3 feet deep to even reach the deckplates. This means the whole torpedo room would have been flooded with at least 6.000 gallons of water, rendering the boat likely completely unstable, unfit to dive and overflooding the batteries in the room next to it, which released poisonous chlorine gas when in contact with sea water. Not to mention that this much water could only have been caused by a major leak, but neither Germans or Americans seem to be particularly concerned by any leaks or by the amount of water in the boat.
Factual error: When Tyler asks Tank "what's the status of the torpedo tube?" His hand is on the periscope tube and it spins freely That tube has many seals on it and is stiffer then that.
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)