“In 1963, a U.S. Navy destroyer is on a routine patrol off Guadalcanal when sonar picks up a sound beneath the waves; the crew say that it sounds like something banging on metal.
They discover a submarine on the ocean floor, but inquiries to naval command reveal no recent sinkings in the area. A joking suggestion from some of the crew that the sub may be haunted sends an anxious and bewildered Chief Bell, who has been feeling unwell for a couple of days, into a frenzy of bizarre behavior, including fainting spells. The commander, Captain Beecham, orders the ship’s diver, McClure, to investigate. They find out that it is an American submarine, and the metal sound is coming from inside.
When McClure bangs on the submarine hull, the metal banging restarts in seeming response. Chief Bell begins to see apparitions of dead sailors beckoning him. The ship’s doctor unsuccessfully tries to convince Bell that he is just having nightmares, and reports to the captain that Bell is experiencing effects of psychological trauma usually caused by wartime experiences. He finds a pile of seaweed in the spot where Bell saw the apparitions.
McClure later discovers the number of the submarine, “714”, which Beecham identifies as belonging to a submarine that was sunk during the Battle of the Eastern Solomons, almost 21 years previously. Although stunned at the idea that someone inside the submarine could still be alive, Beecham asks naval command for a submarine rescue operation. Upon returning to the ship, the diver gives Beecham a dog tag he recovered from the ship, which belonged to Chief Bell.
When Beecham shows the dog tag to Bell, he recollects that he was indeed on that same submarine 21 years before during the battle, when it was surrounded by enemy Japanese ships. Bell was a signalman, and dropped a signal light while attempting to change the infrared filter during the night, causing the filter to fall off. As a result, Japanese ships were able to see the submarine and attack it. Bell fell off the submarine amidst the shelling. The captain took the submarine underwater, but it sank due to the Japanese attack.
Bell was later rescued by an American destroyer that came into the area. Bell tells Beecham that he now understands that the dead submarine crew know he is above them right now and are demanding that he join them in death. Bell is overcome by survivor guilt. Despite Beecham’s efforts to explain to Bell that he was not guilty of cowardice or responsible for the sinking of a submarine already surrounded by enemy ships, Bell races to the deck and jumps overboard. The ship’s crew are unable to save Bell or recover his body.
Later, McClure accompanies the rescue mission into the drowned submarine. Upon returning to the ship, he reports to Beecham that he had found the periscope shears cut in half, with one swinging back and forth. When Beecham asks him to confirm that this was the clanging noise they had heard, McClure agrees, but adds that he had also seen the remains of eight dead sailors, one of whom was holding a hammer in his hand.”