Originally filmed in German, all of the major actors could speak English. When the movie was dubbed into English for USA and UK distribution, all of the principal actors actually dubbed their own voices into English.

The bulk of the film's $15 million budget was spent on constructing U-boats. Specifications for the original Type VII-C U-boat were found at the Chicago Museum of Science and Industry. The plans were taken to the original builder of the subs, who was commissioned to build a full-sized, sea-going replica, their first such assignment since the war ended. A second full-sized model was built for interior filming.

The submarine models built for Das Boot were also the ones used in Raiders of the Lost Ark (1981).

To simulate the storm in the Atlantic, a model of the tower was splashed with water from a large tank. Actor Jan Fedder lost his grip on the railing and was washed off the model, breaking a few ribs in the fall, one of the other actors instantly shouted "Man Overboard". At first Petersen didn't realize it was an accident but enthusiastically yelled "Good idea, Jan. We'll do that one more time!". Peterson still kept the scene and rewrote Jan Fedder's part in the film, so that his character spent a short portion of the movie in bed. The actor actually had to be brought back and forth from the hospital every day because of concussion. The painful expression on his face is real and not acted. (The scene which features him bedridden is available on the uncut edition.)

The movie was shot silent (because of exaggerated camera noise in the submarine interiors) and all German and English dialogue had to be looped.

Because the original TV mini-series was severely criticized in Germany for portraying World War II Germans sympathetically, the producer greeted the first American showing of the film at the Los Angeles Film Festival with great trepidation. They weren't sure how a former enemy nation in that war would react to the film, especially in a city with a large Jewish population, and their fears were reinforced when the audience applauded the opening caption saying 30,000 of 40,000 German men that went into war in submarines didn't come back. However, when it ended, the audience gave the film a standing ovation in appreciation of the artistry of the filmmakers.

The cast was deliberately kept indoors continually during the shooting period in order to look as pale as a real submarine crew would on a mission at sea.

The full-scale model was little more than a hollow shell with an engine, and could be used only in calm waters. While it was being filmed in rougher weather, it cracked in two and sank. It was later recovered, patched with wood planks and used for the final shots.

To help his actors convey the claustrophobic conditions found on a real U-boat, director Wolfgang Petersen insisted on filming within the actual confines of the ship (scarcely wider than a man's outstretched arms), rather than removing the model's outer wall.

In the scene in the La Rochelle bar, Otto Sander (Thomsen) was really drunk.

The picture was nominated for six Academy Awards which was at the time the highest number of Oscar nominations ever received by a foreign language film. The record has since being beaten by such films as Life Is Beautiful (1997) and Crouching Tiger, Hidden Dragon (2000).

Steadicams were not yet in use during the production of the movie. In order to get the fast tracking shots through the U-boat without a shaky image, director of photography Jost Vacano created a system of heavy gyroscopes together with his father that kept the camera steady as he ran through the hallways. The set of the U-boat had intentionally been built slightly bigger to give Vacano more room to work. Even so, as he had to look through the camera, he had to wear a helmet because he would regularly bump his head.

One of the few foreign language films that is primarily referred to on the American market by its original foreign title rather than its translated English title.

To get one particular interior shot, a section of the model's wall was removed. However, Wolfgang Petersen and cinematographer Jost Vacano felt that it detracted from the film's overall authenticity, and from then on only ever filmed the interior from within the confines of the boat.

When Wolfgang Petersen set out to cut down the German TV mini series version of the film to the 3 hour 26 feature director's cut, he discovered that the original music soundtrack had been lost due to film melt. Original soundtrack composer Klaus Doldinger painstakingly archived all the original soundtrack and remixed all the music cues that had been melted in 6 track format. Music editors then had the unenviable task of re-cutting the music to fit the new feature length of the film.

The names of the Captain, Chief Engineer, 1st Watch Officer and 2nd Watch Officer (4 of the 5 main characters) are never given.

Scenes were shot in sequence so that the growth of beards would be entirely natural, although a few shots had to be redone later on with false hair.

The human figures on the 35 foot model were modified Barbie (or rather Ken) dolls.

A miniature submarine was used for scenes in which we see the submarine from outside. The model was steered from the inside by a diver. After three days, the diver who was hired to steer the model had to quit. He had gotten sea sick for the first time in his two-decades-spanning career.

The character of Phillip Thomsen is very loosely based on Heinz Hirsacker, the real life commander of U-572. Hirsacker was not as noble or brave as Thomsen is portrayed in the film and was never awarded a combat decoration for his U-Boat service, much less the Knight's Cross. He was further accused in 1942 of cowardice before the enemy after repeatedly avoiding enemy ships and retreating to base at the first sign of pursuit. Hirsacker was convicted by a court martial and sentenced to death, but committed suicide in 1943 before the sentence could be carried out.

Rutger Hauer was offered to play the Captain, but turned it down to do Blade Runner (1982).

With production costs of 31 million DM, it was for a long time the most expensive German movie ever made. It was beaten in 2006 by Perfume: The Story of a Murderer (2006), which, however, was a German-French-Spanish co-production shot in English.

Depth-charge explosion effects were created by detonating small explosives in a 5m-deep tank and filming them at 1500 frames per second.

The emblem on the U-96's conning tower is the Laughing Sawfish, the emblem of the 9th flotilla from Brest. It was usually green in colour.

Three scale models were built for special effects work. The first, a 35 foot remote controlled model, could sail in high seas and dive; the other two, 18 feet and 8 feet in length, were used for underwater shots. Scale models of tankers, destroyers and other ships were also built to complete the armada.

Klaus Wennemann, who portrays the Chief Engineer, was forty one years old when the film was produced. The actual Chief Engineer of U-96, Hans Peter Dengel, was just over twenty five during his first patrol onboard the submarine. Dengel survived the war patrol, was promoted to Captain Lieutenant in 1943, and assigned as Chief Engineer of the type IX U-boat U-543. He was killed when the boat was sunk by an allied air attack in July 1944.

The scene in which the navigation officer takes an astronomical sight using a sextant is very accurate. The actor is even filmed rocking the sextant from side to side which is not very known to non sailors.

Unusually for a major motion picture, was filmed largely in sequence.

The only remaining U-boot of the VII-C class wasn't used in the movie because it is a technical monument and memorial which can not only be visited, you can actually get an inside view of the U-995. It's located in Laboe/Germany and was placed there in 1972.

When the submarine leaves port at La Rochelle, all modern craft had to be evacuated from the area, while the various modern structures in the background were disguised with plumes of smoke.

The Captain awards include the Knight's Cross which is worn around his neck and the U-boat War Badge, the former awarded for "extreme battlefield bravery or outstanding military leadership" and the latter was awarded after two successful u-boat patrols The Engineer is seen wearing a German Cross in gold on the right side of his tunic and the Iron Cross first class on the left side. Both were awarded for repeated acts of bravery in combat.

Lothar G. Buchheim was incensed when he first saw the scene of one crew member dancing like some sort of tropical girl while the rest of the crew shouted out catcalls and wolf whistles. He said that no U-boat crew would ever behave in such a way.

While shooting scale models in the Northern Sea, filming was disturbed by doves landing on the submarine.

Several additional scenes were scripted based on the original "Das Boot" novel, but in the end were never filmed due to budget and time constraints. In the original script, the U-Boat departs from St. Nazaire and docks at La Rochelle only at the end of the film due to heavy damage and an inability to reach its home port. The escape out of Gibraltar is also extended somewhat including the U-boat stopping a passenger liner and nearly sinking it, but at the last moment realizing the ship is of Spanish registry. The U-boat also encounters another submarine with an inexperienced crew at the entrance to La Rochelle harbor. The second submarine strikes a mine and the entire crew must be rescued. Finally, the character of Lieutenant Werner is much more heavily explored in the original script, including a love interest where Werner was seeing a French girl and by the end of the film suspected she was a member of the French resistance.

Germany maintained its unrestricted submarine warfare was in response to the Royal Navy's blockade, which was illegal under international law.

Vigo is a coastal city in the Galician province in northern Spain. Two U-boats, U-506 and U-523, are reported to have been sunk near Vigo during the Second World War.

Some of the model sub scenes where shot in a small custom-built pond in the back lot of the Bavaria Film Studios. The same pond was later used in Enemy Mine (1985) and the The NeverEnding Story (1984) (The NeverEnding Story), both also Petersen movies.

In the scene where the radioman tunes the radio and, when music is heard, the Captain screams at him to turn it off: what is playing is "Les Preludes" by Franz Liszt, near its finale.

The real captain of U-96, Heinrich Lehmann-Willenbrock, joined the Navy in 1931 and served as Navigator of the naval tender "Weser" from 1933 to 1935. The name "Weser" appears in the film "Das Boot" as the name of the merchant vessel which the submarine meets for resupply in Vigo, Spain.

The poem Lt. Werner cites when the submarine stuck in the Strait of Gibraltar is "Schlacht - Das Maß" from Rudolf G. Binding ("Einmal vor Unerbittlichem stehen...").

A sixth officer mentioned in the novel, and omitted from the film, is the 2nd Engineer who joins the boat on a training cruise in order to take over for the Chief Engineer at the end of the patrol. The 2nd Engineer does not socialize or dine with the other officers and is immediately dis-liked by the Captain who pledges he will find a way to prevent the man from become the new Chief Engineer. In the film, much of the antagonistic elements of the 2nd Engineer are written into the character of the First Officer.

The real first watch officer of U-96 ("Number One") was Gerhard Groth, who was born in 1917 and immigrated to Mexico as a young boy. As with his character in the film, Groth returned to Germany in the late 1930s and joined the Navy just prior to the outbreak of World War II. He was a U-boat flotilla staff officer before joining his first submarine, U-96, as 2nd Watch Officer. He was promoted to 1st Watch Officer in October 1941 and in April 1942 became Captain of his own boat, U-143. He would serve on three boats as commander before the end of World,War II, after which he returned to Mexico City.

The only surviving class IX U-Boat is in a Chicago museum, so a full-size floating replica of the exterior was built. Clever editing made this look like three different boats in the La Rochelle pens. Before filming began, it was used by Steven Spielberg for Raiders of the Lost Ark (1981). The replica comprised three sections, which started to break apart during filming at sea - in the scene following the crew singing "It's A Long Way From Tipperary", a crack can be seen between the first & second sections, midway between the gun which points forward and the crewman with his arms down. That night the replica was blown out to sea and destroyed, but enough parts were salvaged from the surrounding beaches to reconstruct about 2/3rds of the replica, though this now required some extra flotation devices.

The film omits references to a scene in the novel where Lieutenant Werner reads some of the First Officer's diary and in fact gains respect for the man who is otherwise generally disliked by the other officers.

When this was originally mooted as a German-US co-production, Robert Redford and Paul Newman were both considered to play the part of the captain.

The film's opening prologue states: "La Rochelle, France. Autumn, 1941. Germany's vaunted U-boat fleet, with which Hitler hoped to blockade and stamp out Britain, is beginning to suffer its first major setbacks. British freighters are now sailing the Atlantic with stronger and more effective destroyer escorts, inflicting heavy losses on the U-boats. Nevertheless, the German High Command orders more and more U-boats, with ever younger crews, into battle from their ports in occupied France. The battle for control of the Atlantic is turning against the Germans. 40,000 German sailors served on U-boats during World War II. 30,000 never returned."

La Spezia, a city in the Liguria region of northern Italy at the head of La Spezia Gulf, is one of the major Italian military and commercial harbours and is located between Genoa and Pisa. It has been a major naval base since the 1800s.

Given that the convoy is attacked under a full moon, and after this, the crew expected to be given leave for Christmas, odds are that evening is either November 3rd, 4th or 5th, or perhaps Dec. 3rd, 4th or 5th. Those were the dates for the full moon in Nov. & Dec. 1941.

The U-505, a type IX U-boat similar to the one in the film, however it was much larger and designed for longer Patrols. This only surviving variant can be toured at the Chicago Museum of Science and Industry.

Germany's unrestricted submarine warfare in both world wars was in response to the Royal Navy's blockades, which were widely considered illegal under international law.

The sailors who urinate into the road are actually spraying water through small hoses.

Included among the "1001 Movies You Must See Before You Die", edited by Steven Schneider.

Another actor was originally cast as Thomsen, but quit not long after filming began. The shot of Thomsen saying "Hail and victory and sink 'em all!" to the crew of U-96 was re-shot with Otto Sander outside the studio in Munich.

The scenes with the 35 foot (1/6th scale) model were filmed at 55 frames per second.

The only film that year to be Oscar nominated for Best Director, but not Best Picture.

Was originally to be directed by Don Siegel for German producers.

Wolfgang Petersen supervised the director's cut of the film around the same time he was making Air Force One (1997). It premiered on April 4th, 1997, after Air Force One wrapped filming.

The film, as well as the book by Lothar G. Buchheim on which it's based, are both loosely adapted from the wartime career of the Type VIIC boat U-96, and its skipper, Heinrich Lehmann-Willenbrock. In late 1941, Buchheim, who was then a war correspondent in the German Navy's propaganda office, joined the crew of U-96 for one tour in the Battle of the Atlantic. This tour became the basis of Buchheim's book. (In the film, the character Lt. Werner is based on Buchheim.) During the war, Capt.-Lt. Lehmann-Willenbrock ranked seventh among U-Boat skippers in terms of shipping tonnage sunk (183,223 tons on three boats, the U-5, the U-96, and the U-256). After transferring to a new skipper, the U-96 was retired on 5 February 1943, one of the few U-boats to actually survive its tour of duty in the Atlantic. Far from being killed in an air attack (as depicted in the film), Lehmann-Willenbrock survived the war, and later served as captain on various German merchant cargo ships. Lehmann-Willenbrock and Buchheim both served as technical advisers for this film (although the volatile Buchheim fell out with director Wolfgang Petersen, who refused to let the author write the script based on his book). Lehmann-Willenbrock died in Bremen in 1986. Buchheim died in Bavaria in 2007.

For the scene when the boat returns to La Rochelle, most of the extras in and around the sub pen were French. Wolfgang Petersen stated that he, the crew, and the main cast members could feel the tension in the air, as there was still some lingering resentment towards Germany over their treatment by the Nazis during the war. But he also said they did an outstanding job when the time came to film the British air raid on the harbor.

At the end of the film, when a group of bombers attacks La Rochelle, a group of heavy bombers breaks formation. This particular shot (with German WW2 Heinkel 111 bombers) was bought from the movie Battle of Britain (1969).

Wolfgang Petersen's wife, Maria, came up with who was to be killed in the film's conclusion.

When Werner first comes aboard the U-Boat, he is given an oxygen mask along with a survival gear kit, but told by the crew members that it's all "just for show". The mask does in fact save his life when the boat is damaged and the crew has to conserve air.