Skip Beard, listed as a Technical Advisor, served as the Commanding Officer of the real USS Alabama (SSBN 731). He can be seen in the Board of Inquiry scene. He is the man with no hair sitting next to Jason Robards.
Al Pacino was originally offered the role played by Gene Hackman. Warren Beatty was also interested in the movie and producers Don Simpson and Jerry Bruckheimer went through a long period trying to convince him to sign on, before all parties moved on.
The name of the submarine is the "Alabama." The University of Alabama's football team is called "The Crimson Tide," once led by famous coach Paul "Bear" Bryant. In the film, "Bear" is the name of the Alabama's captain's dog.
Quentin Tarantino was brought in to do uncredited "punch-ups" of the dialogue. His major contribution was the comic book bickering. The character name "Russell Vossler" is a reference to Rand Vossler, with whom Tarantino used to work at a video store. See also Pulp Fiction.
Jason Robards, who plays the admiral in the inquiry scene, actually served in the Navy during World War II and received the Navy Cross (though he is not listed in official rolls of Navy Cross winners, despite the claims some - not he - have made).
There is another USS Alabama, a WWII battleship, permanently docked at Mobile Bay, Alabama, that serves as a museum, which has also been occasionally used as a hurricane shelter. Most recently during Hurricane Katrina in which members of 18 museum employee families took shelter during the storm.
The dockside scene where Captain Ramsey (Gene Hackman) addresses the crew shows the USS Alabama in the background and, after his speech, the crew runs onboard. The sub was actually USS Barbel (SS-580), a conventionally-powered (i.e. non-nuclear) attack submarine originally commissioned in 1959. The sail ("conning tower") is a plywood mock-up that generally matched the real Alabama's. Barbel's original sail not only looked different but had already been removed (the Barbel was about to be scrapped).
Don Simpson and Jerry Bruckheimer originally offered Val Kilmer one of the headlining roles but he declined. Years later Kilmer noted it was one of the few films that he wished he had agreed to be in. The role offered to Kilmer by Simpson and Bruckheimer was never formally specified.
The scene in which the USS Alabama is diving for the first time out of dock, the footage is of the real submarine submerging. Director Tony Scott was following along in a helicopter attaining shots of the ship, herself. When the captain of the Alabama requested that the helicopter cease filming, they submerged, which is what director Tony Scott was hoping for anyway.
The "Sonar" panels constantly depicted in the film are completely false. The movie versions off a dumbed down pseudo radar screen, complete with a sweeptrack and bears absolutely no resemblance to a broadband passive sonar display. This was done to give the audience a more visual feel for the otherwise auditory science of Sonar operation.
When Lt. Cmdr Hunter is relieved of duty, Cpt.Ramsey says "Get Lt. Zimmer in here!" Hans Zimmer composed the films soundtrack and his name was added to the script to pay him honor.
Robert Towne received an urgent call from producers Don Simpson and Jerry Bruckheimer one night regarding a key scene between Denzel Washington and Gene Hackman. They wanted Towne to rewrite the discussion on the nature of war between the two characters, thus setting up a more plausible potential for conflict for the remainder of the film. Such was the urgency of the situation, Towne had to literally dictate his rewrite over the phone to the producers as they recorded his words.
At one point in the film, a sonar operator mentions a Soviet "Akula" class submarine. The Russians (former Soviets) do in fact have Akula class subs. Akula is Russian for "shark".
The only previous film that has been about an American Naval Officer being relieved of command by his Executive Officer was The Caine Mutiny, in which Humphrey Bogart played the Captain. Bogart and Jason Robards, who appears in this film, have both been married to Lauren Bacall.
The disagreement between Cpt. Ramsey and Lcdr. Hunter over the origin of the Lipizzaner stallions throughout the movie foreshadows and illustrates the fundamental source of friction between the two men, both insisting that their mutually exclusive version of reality is the truth. Ironically, Cpt. Ramsey, (who believes the stallions are Portuguese) or Lcdr. Hunter (who says they are Spanish) are both incorrect. The Lippizaner stallions are in fact Slovenian - they originate from a town called Lipica.
The cigars that 'Capt. Frank Ramsey' and 'Lt. Commander Ron Hunter' smoke at the beginning of their mission are made by Montecristo. The brand is made in both Cuba and the Dominican Republic, by two totally different companies. But Ramsay's "more expensive than drugs" comment implies that theirs were the Cuban-made variety. Ramsay's cigar of choice throughout the movie is the classic tapered Montecristo #2.