The destruction of the underwater city utilized stock footage from Kaitei gunkan (1963).
Star Vincent Price didn't see the script until six days before shooting began.
John Le Mesurier replaced Boris Karloff in the role of the Reverend Jonathan Ives.
This filmed adaptation of an Edgar Allan Poe source poem was green-lit with the intention on cashing in on the 1960s cycle of Poe pictures. This had been a decade which had already featured seven Poe pictures first released prior to this 1965 movie and every one of them had starred Vincent Price who also headlined this Poe picture.
Actress Susan Hart stated that this movie's screenplay written by Charles Bennett was significantly re-written [by screenwriter Louis M. Heyward].
The place where the city under the sea was located was off the coast of Cornwall, England.
There were creative differences and production conflict between producers Daniel Haller and George Willoughby according to actress Susan Hart and screenwriter Louis M. Heyward
Screenwriter Charles Bennett had previously co-written with Irwin Allen the movie script for Voyage to the Bottom of the Sea (1961).
According to screenwriter Louis M. Heyward, producer George Willoughby left the production of this movie after his script re-write which included additional humorous script changes.
The film's title was changed from the name of its source Edgar Allan Poe poem "The City in the Sea" to the similar War-Gods of the Deep (1965) with this motion picture having also been known as "City Under the Sea".
This movie is alternately titled in English speaking territories by at least three or four different titles: "City in the Sea", "The City Under the Sea", and "War-Gods of the Deep" (aka "War Gods of the Deep").
The movie was made in the style and tradition of the Disney filmed adaptation of Jules Verne's 20,000 Leagues Under the Sea (1954). Actor Vincent Price had previously starred as Robur in Verne's Master of the World (1961) around four years earlier. Further, Verne's Master of the World (1961) and Verne's 20,000 Leagues Under the Sea (1954)_ have more similarities than the two (and technically three) Verne books that the two Verne movies are based on. Moreover, in Italy, this War-Gods of the Deep (1965) movie, was entitled "20,000 leghe sotto la Terra" which translates into the English language as "20,000 Leagues Under the Earth".
The film was made and released about 120 years after its source poem "The City in the Sea" by Edgar Allan Poe had been first published in 1845 and about 134 years after Poe's earlier version of the poem entitled "The Doomed City" had been first published in 1831.
One of around a dozen of filmed Edgar Allan Poe adaptations starring actor Vincent Price that were made and first released during the 1960s era.
The picture was distributed in New York City as part of a double bill with Beach Blanket Bingo (1965).
Actor Vincent Price later played Professor Multiple in "The Deadly Dolls" episode of the fourth season of Voyage to the Bottom of the Sea (1964) [See: Voyage to the Bottom of the Sea: The Deadly Dolls (1967)].
Screenwriter Louis M. Heyward re-wrote the movie's screenplay particularly instructed to add humor stating that the comical character of Harold Tufnell-Jones (played by David Tomlinson) was added by him.
This motion picture was only loosely based on its source Edgar Allan Poe poem "The City in the Sea" (1845).
Final theatrical feature film of actor Henry Oscar who was billed as "Harry Oscar".
The movie's source poem "The City in the Sea" (1845) by Edgar Allan Poe is recited at the end of the picture.