The 3 Oct 1963 DV included the film under its working title, City in the Sea, in a list of upcoming productions by American International Pictures (AIP). The film was one of several in a series based on the works of Edgar Allen Poe. Although the 14 Nov 1963 DV announced Jerry Sohl as screenwriter, he was later replaced by Charles Bennett, as noted in the 18 Feb 1964 LAT. The 14 Feb 1964 DV reported the casting of actress Martha Hyer in a lead role. Six months later, she was replaced by studio contractee Susan Hart, according to the 31 Aug 1964 issue. Various sources state that Hart was also the wife of studio founder James H. Nicholson. Boris Karloff complained to the 30 Dec 1964 Var that he was required to grow a beard for his role, which was eventually taken over by Vincent Price.
       Principal photography began 9 Nov 1964, as reported in that day’s DV. The 22 Feb 1965 edition announced the new title as Warlords of the Deep, for which a second unit was filming underwater scenes in the Bahama Islands. Although the 28 Oct 1964 Var listed Dale Robertson among the cast, the next day’s DV revealed that he had been replaced by Tab Hunter. Filming took place at Pinewood Studios, near London, England, according to the 30 Dec 1964 Var. The picture featured stuntman Peter Brace as AIP’s latest creation, “The Gillman,” a scaly “half human, half fish,” with webbed feet and “claws instead of hands.” A similar monster, known as the “Gill-man,” was conceived more than ten years earlier for The Creature from the Black Lagoon (1954, see entry).
       The film, re-titled War-Gods of the Deep, opened 2 Jun 1965 in New York City, on a double bill with Beach Blanket Bingo (1965, see entry). Critic Howard Thompson described the former picture as the “less bad” of the two. The 2 Jun 1965 DV was more enthusiastic, noting “excellent direction and special effects, plus good performances.” The Los Angeles, CA, opening followed on 28 Jul 1965 at forty locations. The picture screened a year later at the International Science Fiction Film Festival in Trieste, Italy, as noted in the 13 Jul 1966 Var.
       Released in England as City Under the Sea, the picture bore no relation to a Regal Films production of the same name, mentioned in the 12 Jul 1966 DV.