The voice of Todd Armstrong, who played Jason, was dubbed by British actor Tim Turner. Turner's voice was well known as the narrator of the '60s Rank series "Look At Life"'. He was also the narrator of trailers in many British films in the '50s, '60s and '70s, including the one for this movie, and provided the voice of Dr. Peter Brady, the titular hero of the popular late '50s British TV series, H.G.Wells' Invisible Man (1958).
While filming footage of the Argo off the coast of Italy, shooting was interrupted when a replica of the Golden Hind sailed into view. The British television series Sir Francis Drake (1961) happened to be filming in the same location. Producer Charles H. Schneer shouted, "Get that ship out of here. You're in the wrong century!" at the British crew, dispelling any tensions that arose from both shots being lost.
Presumably in order to capitalize on the success of The 7th Voyage of Sinbad (1958), Ray Harryhausen originally conceived of the film as "Sinbad in the Age of Muses". The story would still have been set in ancient Greece and would have involved Sinbad joining Jason in the search for the Golden Fleece.
This British / American film was filmed and released in the waning years of the Italian-produced sword-and-sandal / mythological muscleman movies. Many of those productions dealt with Jason. Most unusual for the time was the casting of British actor Nigel Green as Hercules. Although he was very tall, he lacked the bodybuilder physique that moviegoers were used to seeing for this character. Although film was not able to match the scale of spectacle of the European productions, the elaborate special effects by Ray Harryhausen gave it the look of a more expensive production, contributing to its box-office success.