Ray Harryhausen stated in his biography that this is his least favorite of his films.
The scene of a "destroyer" blowing up is actually stock footage of the sinking of HMS Barham, which occurred on 25 November 1941. To not upset the British public, the Royal Navy decided to withhold an announcement until later; however, in late November 1941 a Scottish medium, Helen Duncan, who had heard of the sinking through a friend, disclosed the sinking during a seance. She was eventually tried under the British Witchcraft Act, the last person before it was repealed.
This science-fiction movie was "suggested" by the 1953 non-fiction book "Flying Saucers From Outer Space" by retired U.S. Marine Corps Maj. Donald E. Keyhoe, who believed that certain aerial phenomena were interplanetary in origin.
One of the scenes of a saucer attacking jets is actually based on footage of an air show crash.
The supposed satellite launches are actually stock footage of Viking rockets, high-altitude probes that were the predecessors of the Vanguard, intended to be the first satellite launcher. The later shots of rockets crashing at takeoff are really German V-2s, since none of the first 12 Vikings ever failed. Ironically, the 13th Viking, now called Vanguard, blew up on the launch pad, just like in the movie.
Columbia's publicity department created publicity stills using the cut-and-paste technique. The resulting stills of the flying saucers were vastly inferior to the special effects in the film itself. In fact, one of the more infamous stills shows Hugh Marlowe and Joan Taylor standing on top of the water in the middle of the Potomac River.
The footage of the bomber exploding is actual WW2 footage of a B-29 Flying Fortress (see also goofs entry).
Fans of Disneyland might recognize the voice of the narrator (and of the alien) as actor Paul Frees, who provides the voice of the ghostly host for The Haunted Mansion ride. Frees also was voice for many cartoon characters for Disney, as well as for Rocky and His Friends (1959).
One of the buildings struck by crashing flying saucers is Union Station, Washington's main train station. This may have been inspired by a 1953 accident when a runaway passenger train smashed into the station concourse.
Bernard Gordon was one of the screenwriters, but was originally credited as "Raymond T. Marcus" because of the Hollywood blacklist. For the 2008 DVD release his real name was restored to the credits, and he was moved from second billing to top billing (over George Worthing Yates).
This was the last movie in which Ray Harryhausen used stop-motion to create collapsing buildings. He said it was too much work.
Whilst Dr. Marvin, his wife, the major and the police officer are being transported in a saucer, a large view screen is displaying their movement away from earth. One of the shots displayed is of earth and the moon with a haze-like fog. This shot is taken from the opening credits of "The Day the Earth Stood Still". Actor Harry Lauter, who played the generator operator in "Earth v The Flying Saucers" also played the tank soldier in "Day the Earth Stood Still" that Klaatu handed the damaged device to that "would have allowed the President to study life on the other planets".
The car that Dr. Marvin and his wife drive is a 1955 Mercury.
The saucer shooting down a plane (real footage from an air-show crash) was also used in the closing credits of the movie "Fury" (2014) under the billing of director of photography Roman Vasnayov.
Opening credits: The characters and incidents portrayed and the names used herein are fictitious and any similarity to the name, character or history of any persons, is entirely accidental and unintentional.
When Carol Marvin is invited to test the alien language translator, she recites "The quality of mercy is not strained/It droppeth as the gentle rain from heaven" into the microphone. Although someone identifies the source as Shakespeare a moment later, the play is not named. The lines are from "The Merchant of Venice," Act IV, scene 1. It is the beginning of Portia's most famous speech in the play, speaking to the plaintiff, Shylock, while she is disguised as a "young male doctor of law" named Balthazar.