Def-Con 4

Def-Con 4 is a 1984 Canadian post-apocalyptic film about three astronauts who endure World War III while stationed on a secret orbiting weapons platform, then return to Earth to find it transformed. The title borrows from the U.S. military's DEFCON alert system, but gets the levels wrong: DEFCON 4 is actually the second-lowest state of readiness, not a high one.

The story begins with text claiming that a perfect nuclear defense system has made global conflict unthinkable. On day 407 of the Nemesis Mission, the crew—Cecil Howe, Walker, and Eva Jordan—monitors rising tensions after Libyan terrorists hijack a U.S. ship carrying Tomahawk missiles. A missile lands in a Soviet city without detonating, then all contact with the ground is lost as news reports describe nuclear explosions in several Soviet cities. The astronauts witness what appears to be a full nuclear exchange between superpowers.

A month later, Howe receives a radio broadcast from his wife, who describes her rural community's survival: many residents, including his sister, were blinded by the blast; radiation sickness is spreading; she is ill; and their infant has died. Two months after that, the spacecraft's guidance system is mysteriously reprogrammed, forcing an emergency return. The crew sets their remaining nuclear payload to detonate in 60 hours and jettisons all but one missile. The capsule crash-lands on a beach in eastern Nova Scotia. Jordan is knocked unconscious. Hearing knocking, Howe and Walker try to dig out, but Walker is pulled from the capsule and eaten by "terminals"—humans driven mad by radiation and starvation.

Hours later, Howe leaves a message for the still-unconscious Jordan and goes for help. He meets Vincent "Vinny" Mckinnon, a survivalist living in a fortified house, and offers the capsule's four-month food supply as a bargaining chip. He also finds Jacelyn "J.J." Jameson, a prisoner in Vinny's home. Using an armored tractor, the group returns to the beach but is ambushed by survivors from a nearby military fort. They are taken to the fort, run by Gideon Hayes—J.J.'s boyfriend and son of a high-ranking naval officer.

Attempting to flee to a government shelter by helicopter, the group is hit by an electromagnetic pulse from the nuclear explosions. Survivors include Gideon, J.J., Marine Corporal Lacey, and Boomer, a Navy technician paralyzed in the crash.