Ray Harryhausen stated in his biography that this is his least favorite of his films.
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.
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.
One of the scenes of a saucer attacking jets is actually based on footage of an air show crash.
The scene of a "destroyer" blowing up is actually stock footage of sinking of HMS Barham which occurred 25 November 1941. To not upset the British public, the Royal Navy decided to withhold an announcement until much late; however, in late November 1941 a Scottish medium Helen Duncan, during a seance disclosed the sinking. She was eventually tried under the British witchcraft act.
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.
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.