Unknown by Zateyev (who is the basis for the character "Captain Alexei Vostrikov" in the film), K-19 had three potentially fatal strikes against her on that summer day. The ship, a "Hotel 1" class (Project 658) submarine, had a design flaw in her steam plant. Moreover, the ship’s power source, two liquid metal nuclear reactors, had no emergency backup system to prevent reactor overheating in the event of a malfunction. And there was something else neither the captain nor his crew knew. A welder had failed to follow safety procedures when he installed the reactor’s primary cooling loop pipelines.

As K-19 made her way in the Norwegian Sea, not far from the island of Jan Mayen, the submarine’s early morning routine was disrupted by the screeching of an alarm. The worst possible event was unfolding: Reactor Number Two had experienced a sharp drop in pressure in its cooling loop.

Unless clear thinking and courageous action intervened, the reactor’s core (including its nuclear fuel) could meltdown. And if THAT happened, a nuclear explosion would likely follow.