When William Shatner and Joan Collins are walking together on the street, they pass in front of a shop with the name Floyd's Barber Shop clearly painted on the window. This is the same Floyd's Barber Shop which is often seen on The Andy Griffith Show (1960), adjacent to the sheriff's office, in the town of Mayberry.
One of only two times in the original series a "curse word" is heard, when Kirk says, "Let's get the hell out of here" at the very end. The second is in Star Trek: The Doomsday Machine (1967), when Kirk sees the Enterprise being drawn into combat, he says; "[What] the hell's going on?".
When asked in February 26, 1992 interview whether the makers of this episode consciously intended it to have the contemporaneous anti-Vietnam-war movement as subtext, associate producer Robert H. Justman replied, "Of course we did."
In Harlan Ellison's original story, Beckwith's change of the past is revealed by members of the Enterprise team who are beamed back to the ship, only to find it is now a pirate vessel named the Condor. This idea was later used in Star Trek: Mirror, Mirror (1967).
This was the most expensive episode produced during the first season, with a budget of $245,316, and also the most expensive episode of the entire series, except the two pilots. The average cost of a first season episode was around $190,000. Also, production went one and half days over schedule, resulting in eight shooting days instead of the usual six.
Early drafts for Harlan Ellison's teleplay "City on the Edge of Forever" included a guest character, Beckwith, an Enterprise crew member who dealt in addictive "Jewels of Sound". It was Beckwith who escaped into the past, via the Guardian of Forever. Gene Roddenberry asked him to change this element, on the grounds that no member of *his* crew would ever use or deal in illegal drugs. According to Ellison's account in the book "Harlan Ellison's the City on the Edge of Forever: The Original Teleplay That Became the Classic Star Trek Episode", for years after the series was canceled, Roddenberry said Ellison's original draft had been unusable because "he had Scotty dealing in interplanetary drugs" - although Mr. Scott does not even appear in that draft.
Clark Gable, who was by no means a leading man in 1930, was not the original choice of reference. The final shooting draft of this script has Edith reference "a Richard Dix movie", but the crew on the set felt Dix's name wouldn't be familiar to viewers in the 1960s.
When Kirk gazes upwards, the star pattern changes. This was mistaken as an error before the fade-out of Act One. The starscape effect was to visualize for audiences that no starships (at least from Starfleet) exist in the present.
After Kirk and Spock talk about the "flop", the scene changes to a street view, where a kosher meat store, with a conspicuously large Star of David on its front, is displayed in the center of the scene. This is one of the very few times a human (Earth) religious symbol is displayed in this series.
Harlan Ellison's original script was extensively rewritten by D.C. Fontana at Gene Roddenberry's behest. Ellison was very unhappy about this, even though the episode won numerous awards (including Hugo Award for Best Dramatic Presentation) and is regarded as one of the classics.
In Harlan Ellison's very first story outline, Beckwith was sentenced to death after he murdered LeBeque, and Kirk ordered his execution to take place on the next deserted planet the Enterprise comes across. Hence, they beam down with Beckwith and a firing squad to the Guardian Planet. This was very soon eliminated from the story.
The title of this episode refers to both the dead city on the time planet and New York itself, where the timeline will either be restored or disrupted. In Harlan Ellison's original script, Kirk, upon first seeing the city sparkling like a jewel on a high mountaintop, reverently says it looks like "a city on the edge of forever". In Ellison's first treatment for this episode, the city they travelled back in time to was Chicago.
Harlan Ellison also wrote scenes in which the regular characters acted very much unlike their usual behavior. For example, Kirk and Spock got into a heavy argument when Spock, witnessing a street speaker calling out against foreign immigrants, called the human race barbaric. Kirk then claims he should've just left Spock to be lynched by the mob.
Originally, then-story editor Steven W. Carabatsos got the job to rewrite Harlan Ellison's script, but his draft was not used. Instead, Ellison agreed to make a rewrite himself, which was again deemed unsuitable. Producer Gene L. Coon also got himself into the rewriting. Finally, the new story editor, D.C. Fontana got the assignment to rewrite Ellison's script and make it suitable for the series. Fontana's draft was then slightly rewritten by Roddenberry to become the final shooting draft. Much of the finished episode is the product of Fontana, who went uncredited (as did all the other writers) for her contribution. Only two lines from Ellison's original teleplay survive in the final episode, both spoken by the Guardian: "Since before your sun burned hot in space, since before your race was born," and "Time has resumed its shape."
Harlan Ellison's original story also described the architecture of the city of the time portal as "covered with strange runes". Somehow, this was interpreted as intending for the city to be depicted as being covered by the remnants of architectural ruins when visualized for the filming on set.
In one scene in this episode, a poster can be seen advertising a boxing event at Madison Square Garden featuring "Kid McCook" vs. "Mike Mason". For Star Trek: Deep Space Nine: Past Tense: Part 2 (1995), scenic artists Doug Drexler and Michael Okuda created a near replica of this boxing poster for a scene set in 1930 San Francisco; the DS9 poster features the same boxers, and says that it is "their first rematch since Madison Square Garden".
The network heavily objected to Kirk's last line, "Let's get the hell out of here" and wanted it to be removed from the episode. The word "Hell" was used four times in The Original Series, the other three being Star Trek: Space Seed (1967), when Kirk quotes Milton, "It is better to rule in Hell than serve in Heaven", Star Trek: The Alternative Factor (1967), when Lazarus tells his counterpart, "I'll chase you into the very fires of hell!", and Star Trek: The Doomsday Machine (1967), when Decker describes the berserker as "right out of hell." This marks the only time that the word was used as an expletive, rather than a reference to the domicile of the damned.
At the very end of the storyline, the crew transports back up to the ship, with the Guardian portal in the background. In the old original edit, the wisps of smoke emanating from the portal freezes at the moment the crew begins to dematerialize, and then the smoke begins moving again as the crew finally disappears. Obviously due to the limitations of the special effects techniques of the 1960s. In the newer released version, with updated special effects edits, the wisps of smoke from the portal continue to move smoothly, throughout the whole transport sequence.
Harlan Ellison's original story outline and first draft script did not feature Dr. McCoy, but an Enterprise crewman named Beckwith, who was dealing drugs among the crew. Beckwith murdered a fellow crewman named LeBeque, who was on the verge of turning him in, escaped to the planet the ship was orbiting, and went through the Time Vortex, operated by a mysterious ancient race called "The Guardians" and changed history. The Enterprise was gone, and a savage pirate ship called the Condor was in its place, full of renegade humans. Kirk and Spock follow Beckwith through the time portal to 1930 New York City, where Kirk falls in love with young social worker Edith Keeler (Koestler in the story outline). Finally, with the help of a legless World War I veteran called Trooper (who dies during the episode's action), they find Beckwith. In the end, Kirk does not stop him saving Edith: he freezes at the crucial moment and Spock prevents her rescue. In a brief epilogue, Spock visits Kirk in his quarters and attempts to console him, saying that "No other woman was offered the universe for love."
Director Joseph Pevney couldn't complete all scenes scheduled to be filmed at 40 Acres on schedule. However, the backlot was already booked for filming by The Andy Griffith Show (1960), so the arrival of McCoy to the past and Rodent's death had to be filmed on a studio alleyway behind Desilu Stage 10.
During the speech scene in the Mission where Kirk and Spock have sat down with their soup, the director repeated (and slowed down) several close-up shots of Spock and Kirk, taken from later in the scene, and used them as reaction shots during Edith's prognostications.
Gene Roddenberry apparently denied Harlan Ellison's pseudonym request because he knew everyone in the science fiction community was aware that the "Cordwainer Bird" credit was Ellison's way of signalling his dissatisfaction with the way production people treated what he wrote. It would have meant that Star Trek (1966) was no different than all the other "science fiction" shows in mistreating quality writers, and could have resulted in prose science fiction writers avoiding contributing to the program.
In The Star Trek Compendium, Allan Asherman suggests that the name "Keeler" is derived from the "keel" of a ship, the longitudinal element of a vessel that keeps it held together - much as Keeler herself keeps the time continuum from coming apart. It also could be interpreted as a hybrid of "killer" and "healer"--a reference to her dual role as the focal point of the time flow. In Ellison's first treatment for this episode, Edith's last name was Koestler.
Desilu Stage 11, usually not a Star Trek (1966) stage, was used for filming the mission interiors. The stage was occupied by My Three Sons (1960) previously, but as that series was moved to another location, it became available for the crew to film.
The Guardian of Forever was designed by Art Director Rolland M. Brooks. Normally, set design was the purview of his colleague Matthew Jeffreys, but due to illness, Brooks took over his chores for the Guardian. When Jefferies returned to his duties and saw the donut-shaped set piece for the first time, he reportedly exclaimed, "What the hell is this?!", according to D.C. Fontana. Special effects artist Jim Rugg was responsible for the light effects for the Guardian.
With regards to this episode, Joan Collins has stated, "To this day, people still want to talk about that episode - some remember me for that more than anything else I've done. I am amazed at the enduring popularity of Star Trek and particularly of that episode." Collins adds, "At the time none of us would have predicted the longevity of the show. I couldn't be more pleased - or more honoured - to be part of Star Trek history." Ms. Collins' memory of her Trek experience seems hazy, however. In her 1985 autobiography, Past Imperfect (p. 248) she makes a few errors regarding the episode: for example, in addition to the common mistake of referring to Mr. Spock as Dr. Spock, she identifies her character as Edith Cleaver instead of Edith Keeler, and she also claims that Spock, not Kirk, allowed her character to be killed - a plot point that was not in the version of the script that was actually shot. Most significantly, she claims Edith tried to "prove to the world that Hitler was a nice guy."
Harlan Ellison's script was unusable for the series for many different reasons. Gene Roddenberry objected to the idea that drug usage would still be a problem in the 23rd century, and even present among starship crews. Also, the production staff was heavily against Kirk's final inactivity. It seemed that being unable to decide and act, viewers could never be able to accept him as the strong leader figure in later episodes. Elements, such as the Guardians and the Condor and its crew were simply impossible to create on the series' budget.
Together with Matthew Jeffreys, Jim Rugg was also responsible for Spock's computer-aid to access the information in his tricorder for the episode, as Jefferies recalled, "When a script came out, Roddenberry would say, "I need something that supposedly does such and such...come up with something." So we would work together on the workbench with Jimmy Rugg and see what we could cobble together.", to which Rugg added, "We got a bunch of antique vacuum tubes-real '30s types-and added a few blinking lights among them." Rugg subsequently oversaw its destruction in the episode.
The trivia items below may give away important plot points.
In Harlan Ellison's original story, Kirk and Spock are aided in the 1930s by a vagrant called Rodent who reveals himself to be a veteran of the Battle of the Somme. In the final product, Rodent is the bum who incinerates himself with McCoy's phaser.
Rodent's death is deleted in some rebroadcasts, but is intact in home video editions. When McCoy meets Rodent holding the milk bottle, the scene ends with McCoy collapsing, then cuts to McCoy meeting Keeler in the Mission. In the complete scene, after McCoy collapses, Rodent picks McCoy's pocket and takes his hand phaser (which he took from the transporter chief) and accidentally sets it on overload, killing himself.