DeepStar Six

DeepStar Six is an American science fiction horror film about the struggles of the crew of an underwater military outpost to defend their base against the attacks of a sea monster possibly a giant eurypterid. It was released in January 1989. The films main actors and supporting players included Greg Evigan, Taurean Blacque, Nancy Everhard, Cindy Pickett, Miguel Ferrer and Matt McCoy.

The ensuing detonation collapses part of the seabed, forming a massive fissure in the ocean floor. Submarine pilots Osborne and Hodges Ronn Carroll, Thom Bray send an unmanned probe to explore, but lose contact and venture in after it. Upon finding the probe, they detect a large sonar contact moments before being attacked and killed by an unseen force. The aggressor then attacks the observation pod, leaving Joyce Collins Nancy Everhard and a dying Burciaga trapped inside as it teeters on the edge of the ravine. Captain Laidlaw Taurean Blacque and submarine pilot McBride Greg Evigan who is also Collins paramour attempt a rescue. They dock with the pod and rescue Collins, but the unstable hatch door closes on Laidlaw. Mortally wounded, he floods the compartment, forcing McBride and Collins to return and leave without him.The remaining crew now prepare to abandon the base, but the missile platform must first be secured. Without Laidlaw, facility technician Snyder Miguel Ferrer is forced to interpret the unfamiliar protocol. When prompted by the computer to explain the reason, Snyder reports aggression due to the creature, which the computer interprets as an enemy military force and advises to detonate the missile warheads. He complies and the resulting explosion creates a shockwave that damages DeepStar Six and the cooling system for the bases nuclear reactor. With failed life support, they begin repairs to restore power and pressure for the decompression procedure. ........

Source: Wikipedia