Danger Below is a 1993 action film described as "Die Hard on a submarine" starring Arnold Schwarznegger, Kim Basinger and Michael Ironside.
While out at a romantic dinner, Naval officer Beau Raker learns from his wife Beth that she is in fact pregnant. The couple are overjoyed but get caught in a storm on the way home. Beau spots a man trying to flag them down at the roadside and pulls over to help, only to find that he is one of three carjackers. Beau manages to outsmart them and retrieve his gun, but Beth is shot in the process. Devastated, Beau leaves the Navy.
About one year later, Beau is approached by his old friend, Bruce Conway, to become a submarine consultant on the USS Autumn. Beau is reluctant but after seeing how badly his life has gotten since Beth's death, he decides to go along with it.
On the day he visits the submarine, a nefarious plot is taking form. The traitorous first officer, Kristof, is in cahoots with a terrorist gang led by Eric Sadler. Kristof relates the coordinates of the submarine to Sadler, who then cuts communication between a plane and the airport. He then hijacks it and ditches it into the ocean by the submarine, and then proceeds to murder any survivors who are not part of his gang. The Autumn picks up the gang unknowingly, thinking that they are the only survivors of an air disaster.
Soon enough, Sadler and his gang take control of the submarine, planning to hold the UN to ransom by threatening to fire the on board missiles. A young woman, Jen Sutton, is also on board, posing as an officer when she is in fact the captain's daughter, and is trying to reconcile with him. She manages to avoid detection and then frees Beau, who Kristof had previously locked up after a dispute. Beau begins to work his way through Sadler's gang, dispatching them one by one.
The sadistic Sadler soon realises that Beau was a former officer, and berates Kristof for not smoothing out such a bump in their plans. With his deadline nearing and no sight of payment from the UN, Sadler gets ready to fire the missiles and makes his way to the control room. Beau, meanwhile, liberates the imprisoned crew and they set about retaking the craft. Jen is also reunited with her father but Beau learns that Sadler has fired the missiles so leaves her in charge while setting out to kill Sadler.
Beau heads for the control room and faces Sadler. The two talks for a while before Beau reminds Sadler that he has come to kill him and a brutal fist fight breaks out. Sadler pins Beau down but the hero retrieves a knife and guts Sadler. He then alerts the government and they sent fighter jets to safely blow up the warheads in the water. Meanwhile, Kristof takes Jen hostage leading Beau into a confrontation, but Jen's father sneaks up behind Kristof and manages to gun him down. The film ends.
Arnold Schwarznegger - Beau Raker
Kim Basinger - Jen Sutton
Michael Ironside - Eric Sadler