A History Channel review of the movie which aired soon after its release included a German World War II U-Boat commander. At the end of the show he was asked for his opinion of the authenticity of the movie. His response was; "They got one thing right in the movie. There were U-Boats in the North Atlantic during the Second World War."
The caption before the end credits, detailing the fact that the Royal Navy captured the first Enigma machine, was only added after an outcry in Britain, where it was believed that Hollywood was trying to claim the credit for the Americans (whose forces captured no German Naval Enigma material until 1944).
For authenticity, the stage crew made a working submarine for filming in the Mediterranean off of Malta. During production, an American warship appeared and was so taken in by the Nazi submarine they actually sent an armed team to board it.
In reality, the submarine U-571 was never actually captured. The submarines U-559 and U-110 were the ones captured with the codebooks but by the British Navy in August 1941, four months before the United States entered the war. U-570 however was in fact a u-boat captured in late 1941 (by Britain) near Iceland, and subsequently deployed as HMS Graph until early 1944. Its appearance was used by the Royal Navy to fool German ships and submarines, and destroy them by surprise.
The U-505 submarine is on exhibit at The Museum of Science and Industry in Chicago, Illinois. It is the real U-505-the only German submarine in the United States, and, now, a national memorial to the 55,000 American sailors who gave their lives on the high seas in WWI and WWII.
This movie represents one of a select group of a few World War II submarine movies which have won the one single Academy Award in a technical category, that's just only the one Oscar in either special effects or sound editing. These movies include Crash Dive (1943); The Enemy Below (1957); Torpedo Run (1958) and U-571 (2000). The non-WW II sub-movie, The Hunt for Red October (1990) also won just the one Oscar as did the WW 2 part sub-movie 49th Parallel (1941), but for Best Original Story.
The Germans did in fact introduce a new, 4-rotor version of their Enigma machine in February 1942; and the code was in fact practically unbreakable by the Allies until the capture of associated codebooks from a submarine, in October 1942. 'Shark' (as the Navel Four Rotor Enigma cipher was know by Bletchley Park) was broken regularly from December of that year (sources include Bletchley Park . But in real life this was a British operation and did not involve a deception like that depicted in the film. The sub itself, the U-559, sank shortly after the codebooks were removed.
In the original script, when Tank is discussing the U-571's condition he reports that the submarine has only six tonnes of fuel, which is insufficient to return them to the United States. That is why Lt. Tyler sets a course for England.
When the "U 571" leaves the navy port at the beginning of its turn, marine ships from the former East Germany (GDR) are shown in the background: the so-called "coast mine seekers" (corvettes), built for the east-german navy "Volksmarine" from the late 1960s and in use until the end of the country and the re-unification with the West-Germany (Federal Republic of Germany). These ships (and their slightly larger version "high-sea mine seekers" or corvette "Adler" (= Eagle in NATO jargon)) where able to position, relocate and destroy mines. They mainly served at the sea-frontier between east and west (Nato and Warsaw treaty) in the Baltic sea.
The trivia items below may give away important plot points.
Bill Paxton's final words before his character's death are when he yells to LT Tyler, "Andy! Take her down!" This is taken from a real incident in 1943, when the submarine USS Growler collided with a Japanese destroyer in a night battle. Both ships were badly damaged in the collision, and the Japanese immediately opened fire on the Growler at close range. The Growler's captain, Commander Howard Gilmore, and three other men on the lookout platform were hit by machine gun fire. Gilmore was badly wounded and the others were killed. Knowing that the Growler would be sunk if the Japanese brought their 5-inch guns to bear, Gilmore yelled to his executive officer, "Take her down!" Gilmore drowned when the Growler submerged beneath him, but his sacrifice saved his submarine and the remainder of his crew. Howard Gilmore was posthumously awarded the Medal of Honor.