Ken Kuronuma, who wrote the original story for this film, was inspired by an incident in Kentucky in 1948 when Clapt. Thomas F. Mantell, a pilot for the Kentucky Air National Guard, died in a crash while pursuing what was thought to be a UFO.
The original Japanese film's climactic monster invasion was filmed around, and set in, Fukuoka, the largest city on Japan's southernmost island of Kyushu. However, the American version relocated the action in the dubbing to another city in Kyushu, Sasebo, perhaps concerned that their dubbing actors would sorely mispronounce the word "Fukuoka" at inappropriate moments.
While shooting the scene in which Rodan flies over the bridge in Saikai Village in Kyushu, the pulley from which Haruo Nakajima was suspended broke. He fell from a height of 25 feet, but the wings and the water, which was about one and a half feet deep, absorbed much of the impact.
In the US version, the English dubbing changed the name of the destroyed city, which was actually Fukuoka, to Sasebo because the name of that city was more familiar to Americans since the US had major military facilities there.
The King Brothers attempted to add footage of American Navy and Japanese Maritime Self-Defense Force ships firing their main guns and anti-aircraft batteries at the Rodans (the Kings had switched the city from Fukuoka, which had no naval facilities, to Sasebo, which had them). The brothers wanted footage of joint American-Japanese naval gunfire exercises, but the Pentagon refused, to avoid the Soviets seeing training techniques. Ironically, a year later, in 1957 with The Mysterians (1957), the Pentagon would freely offer stock footage for public relations purposes.
George Takei was the first Japanese-American actor to do voice-overs for Toho's movies. Previously, Chinese-American actors, including James Hong, Sammee Tong and Keye Luke, were used. At the time, Chinese actors had filled a niche in Hollywood, portraying Japanese soldiers and civilians in war movies.
The cable supporting Rodan over Sasebo Bridge snapped, causing the stuntman in the suit to fall 25 feet into the water. The incident is left in the movie as the scene where Rodan dives into the water near the bridge and submerges. Ironically, the cables were reattached for the scene where Rodan lifts off out of the water, but they almost broke again because the suit became waterlogged and doubled in weight.
The bruise that Kenji Sahara has on his left cheek in the cave scene where he first sees Rodan hatch from the egg was real. As Sahara crawled backwards, he turned the wrong way and went face-first into a rock. Despite the injury, he finished the scene.