Def-Con 4 is a 1985 Canadian post-apocalyptic film, portraying three astronauts who survive World War III aboard a space station and return to Earth to find greatly changed circumstances. The film's title refers to the Defense Readiness Condition (DEFCON), the United States military's nuclear alert system, though the title erroneously refers to DEFCON 4 as a high state of readiness. DEFCON 4 is in fact the second-lowest state of readiness.