The "abandoned missile base" in the movie, is actually the Alabama Space and Rocket Center museum, and the "Rocket Park" is in the backlot of the museum. The museum benefitted from the filming of this movie, because the display rockets had to be "aged" for the film, and then later cleaned. The bi-annually cleaning of these outdoor displays is a major expense.
The matte painting that the titles are shown over in the beginning of this movie is the same matte painting the Army of Apes sees in Beneath the Planet of the Apes (1970).
Richard Harris and Ann Turkel were married during the time this movie was made and released. This picture was one of four films the couple made together, the others being Golden Rendezvous (1977), The Cassandra Crossing (1976), and 99 and 44/100% Dead! (1974), with the latter being made and released before they tied the knot.
The movie was filmed entirely on location in the American state of Alabama in the USA.