Morning Departure

During a routine snorkel mast test, the British submarine HMS Trojan encounters an unrecovered WWII magnetic mine. The mine detonates, blowing off the bow and flooding the forward sections. Fifty-three crewmen are killed, leaving twelve alive in the midsection who are saved by watertight doors closed by the captain's orders.

As Trojan remains overdue, surface rescue vessels are dispatched to locate the stricken submarine. The captain expels a quantity of oil to mark the wreck’s position, helping rescuers pinpoint Trojan on the sea surface. Divers prepare to reach the survivors below.

A diver is sent down with an air line to establish a link for rescue operations. The crew and salvage team follow standard escape procedures, positioning breathing gear and readying for a potential lift from the damaged sub. Hope of retrieving survivors remains cautious but persistent.

Armstrong uses a card-draw to determine who will be released first. The cook Higgins and the first lieutenant Manson receive low cards; three crewmen have high cards, with a tie between Snipe and Marks. After a redeal, Snipe loses and goes berserk, requiring restraint, and Armstrong asks Marks to stay behind.

The four chosen crew escape through the gun hatch and are picked up by salvage vessels on the surface. The remaining eight crew assume there will be enough breathing sets for everyone to escape, under the mistaken impression that supplies are sufficient.

Snipe pretends to have hurt his arm to avoid leaving, while Armstrong insists that Marks stay with the others to improve their odds. The tension among the crew deepens as the reality of limited resources becomes clear. The crew below continues to wait and hope for rescue.

Low on air and under stress, Manson experiences a fainting spell, claiming it stemmed from prior malaria. Snipe nonetheless helps, supporting Manson with both arms and continuing to look after him despite the danger. Their bond under pressure grows within the confined submarine.

Divers secure cables beneath the submarine, and the wreck is slowly winched upward at about fifteen feet per day. The operation proceeds with careful coordination as conditions appear initially favorable.

Weather deteriorates into a full storm at sea, causing the submarine to shift on the cables and sink again to the sea floor. The crew's optimism fades as the salvage operation becomes increasingly dangerous and uncertain.

Chlorine leaks from a nearby site infiltrate the surviving compartments, and Manson succumbs to the toxic gas. His death underscores the perilous conditions facing the trapped crew and the fragility of their air supply.

The storm becomes too dangerous even for the salvage crew, and the captain decides to abandon the operation to save his own men. This decision seals the fate of the trapped crew remaining below.

With the salvage attempt halted and the submarine left at the bottom, the remaining crew endure the dire situation. Armstrong reads from a naval prayer book, clinging to faith as the odds of rescue dwindle.

Throughout the ordeal, viewers glimpse the crew's personal lives: Snipe is devoted to a wayward wife whom he idolizes, while Armstrong has been offered a lucrative shore job by his wealthy father-in-law and has contemplated leaving the Navy after this patrol. These tensions add emotional weight to the crisis aboard the submarine.