From OpenwaterpediaJames Cameron, starring Ed Harris, Mary Elizabeth Mastrantonio, and Michael Biehn. When an American submarine sinks in the Atlantic, the US search and recovery team works with an oil platform crew, racing against Russian vessels to recover the ship. Deep in the ocean, they encounter a new and mysterious species. The original musical score was composed by Alan Silvestri. It was released in 1989, in North America.
A US ballistic missile submarine, the USS Montana, sinks near the edge of the Cayman Trough after an accidental encounter with an unidentified submerged object. As Soviet ships and submarines head towards the area in an attempt to salvage the sub, and with a hurricane moving in, the Americans decide that the quickest way to mount a rescue is to insert a SEAL team onto the Deep Core, a privately owned, experimental underwater oil drilling platform, located 2 km below sea level, which will serve as their base of operations. The designer of the platform, Dr. Lindsey Brigman, insists on accompanying the SEAL team, even though her estranged husband, Virgil "Bud" Brigman, is currently serving as the platform's foreman.
As the SEALs and the platform crew attempt to discover the cause of the Montana's failure, they spot strange creatures they cannot identify, only later discovering that the creatures have intelligence and dubbing them "NTIs"—"non-terrestrial intelligence". On orders from the SEAL leader Lt. Hiram Coffey and without the platform crew's knowledge, the SEALs use one of the platform's mini-subs to retrieve a warhead from a Trident missile aboard the Montana. However, they do so at an inopportune time, as the hurricane strikes the surface and they are unable to release the tether from the rig's surface support ship, the Benthic Explorer. Tossed by the storm, the Explorer's entire crane and cable system break off and fall into the water. The crane barely misses the platform when it hits the ocean floor, but falls into the trench, its weight pulling the tether and the whole platform towards the drop-off. The rig hangs up on the very edge of the cliff, preventing a plummet into the depths. Several crew members are lost due to flooding in the platform, while the surviving crew and SEALs tend to wounds and attempt to restore the platform's critical power.
An NTI probe in the form of a living column of water explores the platform, and while the platform crew believes it to be harmless, Coffey sees it as a threat. The platform crew realizes Coffey is suffering from high-pressure nervous syndrome, which is making him paranoid. Using one of the remote operated vehicles to spy on Coffey from outside the platform, they discover he is planning on sending the warhead down into the chasm to destroy whatever may be down there. Bud attempts to subdue Coffey before he can leave the platform in one of the mini-subs, but he is unable to do so. Bud and Lindsey chase Coffey in the station's other sub; they manage to damage Coffey's sub, causing it to fall into the trench, where Coffey is killed when the pressure crushes the vehicle. However, Bud and Lindsey are too late to stop the remote vehicle and its attached warhead, on a pre-programmed course and set to explode within 3 hours, from dropping into the trench. Furthermore, their sub is flooding due to a rupture in the hull. Lindsey realizes that the sub's crippled systems, the distance between the sub and the platform, and the fact that their sole source of oxygen is a backpack and regulator that are hard-mounted to Bud's diving helmet combine to leave just one solution. After being convinced, Bud locks his helmet onto his diving suit, watches Lindsey drown, and then tows her body back to Deep Core, hoping that the cold water shocked her body into deep hibernation. The Deep Core crew, trained and equipped for medical emergencies, is able to restart Lindsey's heart via CPR and a defibrillator. The two reaffirm their lost love.
The crew tracks the warhead, finding the remote vehicle has failed from the pressure and landed on a ledge partway down the trench. The SEALs have brought along special diving equipment featuring a liquid breathing apparatus that would allow for a human to dive that far. However, only one of the two surviving SEALs is trustworthy and his injuries prevent him from using it. Bud volunteers; he will not be able to talk and is instead forced to communicate through a keypad on his suit. Bud begins his 7 km dive into the trench, reaches the ledge where the warhead sits, and is guided by the SEAL in disarming it. However, the dive has taken too long for Bud to return to the top of the trench before the oxygen in the liquid runs out. Bud, aware this could happen, writes that he has only five minutes left, and despite Lindsey's pleas to return, decides to remain on the ledge. He types his love to Lindsey in a final message, saying, "Knew this was a one-way ticket, but you know I had to come. Love you, wife."
As Bud lies on the ledge awaiting his death, bright lights appear below him and he encounters an aquatic NTI. The being reaches out and takes Bud's hand and then leads him even further down to a massive NTI spacecraft sitting 8 km deep in the trench. Deep within the ship, the NTIs provide Bud with an atmosphere that allows him to breathe. The NTIs replay Bud's message to Lindsey for him, and they exchange meaningful looks.
On the platform, believing Bud to be dead, Lindsey and the crew are surprised to find Bud radioing back to them, telling them to get ready. The crew observes something very large quickly rising out of the trench, and sees the lights from the NTI spacecraft as it rises. The enormous ship eventually surfaces, lifting many of the naval ships out of the water and leaving them aground on the NTI ship's hull, as well as the platform itself. Leaving the platform on the surface of the ship, the platform crew and remaining SEALS are surprised to find that they are fine and not suffering from decompression sickness after rising so fast out of the water, and credit the NTIs. Bud emerges from the NTI ship, and he and Lindsey rush to meet each other; engaging in a passionate kiss.