Blue, deep and featureless, the twilight of five hundred feet down. Propeller sound. Materializing out of the blue limbo is the enormous but sleek form of an Ohio-class SSBN ballistic missile submarine. The Montana, a U.S. Navy nuclear missile submarine, operating deep in the Cayman Trough in the Caribbean Sea, encounters an unidentified submerged object.
In the attack center, darkened to womb-red, the crew's faces shine with sweat in the glow of their instruments. The Skipper and his Exec crowd around Barnes, the sonarman. Barnes puts the signal onto a speaker and everyone in the attack room listens to the intruder's acoustic signature, a strange thrumming.
The captain studies the electronic position board, a graphic representation of the contours of the steep-walled canyon, a symbol for the Montana, and converging with it, an amorphous trace, representing the bogey. Tension builds in the attack room as the Montana surges to intercept the intruder. The exec tensely watches the vector-graphic readout for the side-scan sonar array. The sub is running uncomfortably close to the cliff walls. Suddenly the control room lights dim almost to blackness.
The object passes very close to the submarine and the vessel loses power. We see only the effect, not the source, as a large diffuse light passes rapidly over the sub's hull. Moments later a shockwave, like an underwater sonic boom, impacts the sub, slamming it sideways.
The bride crew are knocked off their feet, as the ship is buffeted. Sirens. Everyone shouting at once. The power flickers low. Power returns in time for the sonarman to get a glimpse at the side-scan display... as the sheer cliff wall looms before them.
The cliff wall materializes out of the blue limbo off the port bow with nightmarish slow-motion. The sub slams into it with horrific force, scraping along and bouncing off. One tail stabilizer is sheared off and the big screw prangs the wall with an earsplitting K-K-KWANG!
In the Torpedo Room with the outer tube-doors torn off, seawater slams in, busting the inner hatches. Two-foot thick columns of water, like fire-hoses of the gods, blast into the room. Everything vanishes instantly in white spray.
In the Attack Center, everyone is hurled off his feet. The planesman flights to recover control of the yoke. The great sub is being hauled down by the mass of its flooded bow section, its flanks rushing past us like a freight train headed for Hell. In the Control Room, the command crew fights futility for control, everyone shouting and terrified. The Captain locks eyes with the Exec amid the din and orders him to launch the buoy.
The Exec opens the door to a small box and punches a button. A red light comes on. The Captains takes a deep breath. Outside the Montana, a tiny transmitter is ejected from the sub's hell and begins its long ascent to the surface. A second later the sub slams down like a piledriver onto a ledge, tearing open its pressure hull.
Inside the Montana, seawater blasts down the corridors, explodes across the control room, hurling men like dolls. It floods the cavernous missile bay in seconds. The water bursts through hatches into the reactor room and blasts men out of frame in a micro-second.
In the cobalt twilight we see the Montana slide down the sea cliff, its hull screeching like the death agonies of some marine dinosaur. Descending in an avalanche of silt, it finally disappears into the blackness below... a blackness which continues almost straight down, 20,000 feet to the bottom of the Cayman Trough. The abyss.
Above, in the world, the Caribbean rolling gray under a stormy sky. The Montana's emergency buoy pops to the surface, transmitting.