(written from a Production point of view)
This season saw Ensign Pavel Chekov added to the regular bridge crew. Although his first appearance in "Catspaw" had him operating the science station, "Friday's Child" established him as the ship's primary navigator.
Following their introduction near the end of the previous season, the Klingons were established as major adversaries, appearing in three episodes, "Friday's Child", "The Trouble with Tribbles", and "A Private Little War". The second of those would turn out to be one of the show's most popular and influential episodes, introducing Koloth and the Tribbles, who reappeared on Deep Space 9, with other characters reappearing in the Star Trek: The Animated Series episode "More Tribbles, More Troubles". The Romulans also made a brief reappearance in "The Deadly Years" while Harry Mudd returned for a second tussle with the USS Enterprise crew in the comedic episode "I, Mudd". "Mirror, Mirror" saw Kirk and company paying a first visit to the mirror universe which also later featured prominently on Deep Space 9 and Star Trek: Discovery.
The show began to explore the rest of the Federation, with the Enterprise making its first trip to Vulcan as Spock underwent Pon farr in "Amok Time". "Journey to Babel" saw the Enterprise transporting representatives of the Vulcans, Andorians, and Tellarites to a conference to admit the Coridanites to the Federation, among them Spock's father Sarek. "Obsession" provided an insight into Kirk's early Starfleet career, revealing some of the details of his tour of duty on the USS Farragut.
Although most episodes centered around the triumvirate of Kirk, Spock, and McCoy, the other regular crewmembers began to appear more. After first commanding the ship in "The Return of the Archons", Scotty was firmly established as the Enterprise's third-in-command, with episodes like "Friday's Child", "The Apple", and "Bread and Circuses" giving screen time to his command. He was also given a spotlight in "Wolf in the Fold", in which he was accused of a series of murders. Chekov and Uhura were given a chance to accompany Kirk on an away mission in "The Gamesters of Triskelion" and Chekov also had a prominent role, and an opportunity for romance, in "The Apple". Sulu, on the other hand, was absent from nine consecutive episodes in the middle of the season, the result of a film George Takei was working on over-running.
The Enterprise visited several planets based on Earth history, either by coincidence or as a result of Human visitors, such as Ancient Rome ("Bread and Circuses"), Chicago gangsters ("A Piece of the Action"), Nazi Germany ("Patterns of Force") and the American Constitution ("The Omega Glory"). There were other surprising encounters with Zefram Cochrane, the father of warp technology ("Metamorphosis"), the Greek god Apollo ("Who Mourns for Adonais?") and a giant space amoeba ("The Immunity Syndrome").
The show continued Gene Roddenberry's original idea of political fables, with two episodes identified as providing somewhat opposing commentary on the Vietnam War. "A Private Little War" saw the Federation and the Klingons supporting opposing sides in a civil war, with Kirk talking of the need to maintain the balance of power, while "The Omega Glory" saw Kirk telling a race based around the American Constitution that the values of liberty and freedom of belief also applied to their enemies.
The season closed with "Assignment: Earth", a back door pilot for a proposed spin-off series which saw Kirk and Spock encountering Gary Seven, a man employed by mysterious aliens to watch over 20th century Earth.
- James Doohan as Montgomery Scott
- George Takei as Hikaru Sulu
- Nichelle Nichols as Uhura
- Walter Koenig as Pavel Chekov
- Majel Barrett as Christine Chapel
- Eddie Paskey as Leslie
- Gene L. Coon – Producer ("Catspaw" – "Bread and Circuses")
- John Meredyth Lucas – Producer ("Journey to Babel" – "The Omega Glory")
- Gene Roddenberry – Producer ("Assignment: Earth")
- Gene Roddenberry – Executive Producer
- Robert H. Justman – Associate Producer
- Herbert F. Solow – Executive in Charge of Production
- Edward K. Milkis – Assistant to the Producer
- Gregg Peters – Unit Production Manager
- D.C. Fontana – Script Consultant
- Walter M. Jefferies – Art Director
- Rolland M. Brooks – Art Director ("Catspaw" – "Amok Time")
- John Jefferies – Set Designer
- John Dwyer – Set Decorator
- Joseph J. Stone – Set Decorator
- Jerry Finnerman – Director of Photography ("Catspaw" – "A Piece of the Action"; "Return to Tomorrow" – "Assignment: Earth")
- Keith Smith – Director of Photography ("By Any Other Name")
- Elliot Schick – Assistant Director
- Rusty Meek – Assistant Director
- Phil Rawlins – Assistant Director
- Bruce Schoengarth – Film Editor
- Donald R. Rode – Film Editor
- Fabien Tordjmann – Film Editor
- John W. Hanley – Film Editor
- James D. Ballas – Film Editor
- William Ware Theiss – Costume Designer
- Fred B. Phillips – Make-Up Artist
- Pat Westmore – Hair Stylist
- George A. Rutter – Script Supervisor
- Joseph D'Agosta – Casting Director
- Irving A. Feinberg – Property Master
- Jim Rugg – Special Effects
- Douglas H. Grindstaff – Sound Effects Editor
- Jim Henrickson – Music Editor
- Elden E. Ruberg – Re-recording Mixer
- Gordon L. Day – Re-recording Mixer
- Carl W. Daniels – Production Mixer
- George H. Merhoff – Gaffer
- George Rader – Head Grip
- Ken Harvey – Key Costumer
- Marc Daniels
- Joseph Pevney
- Arch Dalzell – Director of Photography ("Who Mourns for Adonais?")
- Richard C. Datin – Model Maker ("The Trouble with Tribbles")
- Kellam de Forest – Researcher
- Linwood G. Dunn – Visual Effects Cinematographer
- Richard Edlund – The Companion effects artist ("Metamorphosis")
- Al Francis – Camera Operator
- Al Jacoby – Assistant Property Master
- Joseph R. Jennings – Assistant Art Director
- Mike May – Props
- Bill McGovern – Clapper/Loader
- Tiger Shapiro – Second Assistant Director
- Charles Washburn – Second Assistant Director
- Andrea Weaver – Women's Costumer
- There were some "upgrades" to bridge equipment made at the start of this season (most notably the helm console), but these changes aren't always visible because first-season footage was used in many bridge scenes. You can recognize this footage when you see the viewing screen and the back of Sulu's head – the navigator isn't shown because Walter Koenig hadn't signed on when this footage was filmed. The black viewer or scope at Spock's library computer station was replaced with a gray one (that came with a knob on the left side). A similar scope was added to Scott's engineering station.
- For the second season, the production budget per episode was around US$185,000, slightly less than Season 1.
- Lawrence Montaigne, who played Stonn in "Amok Time", and Mark Lenard were both being considered as possible replacements for Leonard Nimoy prior to the beginning of the second season if contract negotiations had fallen through.   Nimoy's agent had asked for Nimoy's salary to be increased from US$1,250 per episode during the first season to US$9,000 for the second season. Eventually a compromise figure of US$2,500 per episode was reached and Nimoy signed on for the second season. (Inside Star Trek: The Real Story, pp. 317-324)
- Dr. McCoy's sickbay gained a lab this season. The back bulkhead of said lab appears to be one of the bulkheads of the SS Botany Bay from "Space Seed".
- A new expanded engineering set was built, including a small set called "Emergency Manual Monitor" built on stilts that looked down onto the engineering set.
- A completely new auxiliary control set was also built.
- In the second season more emphasis was put on the supporting characters (especially Scotty and Chekov), but the show didn't feature scenes of every-day activity around lower decks of the ship anymore as it did in the first season.
- Beginning with Season 2, the episode titles and credits were in the same font as the series title. Also, DeForest Kelley's and Gene Roddenberry's names were added to the opening credits.
- Also, during the opening credits, the Enterprise fly-by and the planet that the Enterprise orbited were different from that of Season 1.
- Walter Koenig joined the main cast as the Russian navigator Pavel Chekov.
- The theme music for the series was slightly re-arranged this season, with Loulie Jean Norman supplying vocal accompaniment.
- Season 2 was a period of behind-the-scenes transition from Desilu to Paramount production. On 15 February 1967, Gulf+Western's purchase of Desilu was announced. It was commemorated with a ribbon-cutting ceremony on 26 July. Gulf+Western executives were known to have signed off on production of the then-upcoming Season 2 of Star Trek, as they would have been financially obligated to continue its production after the sale. Therefore, Season 2 technically began filming as a Desilu/Gulf+Western co-production. (Sanders, Coyne Steven and Tom Gilbert. Desilu: The Story of Lucille Ball and Desi Arnaz. HarperCollins. 1994. 297-298) However, the December 1967 intra-company merger between Paramount Pictures and Desilu caused later episodes of the season to be labeled "a Paramount production". Episodes throughout the season thus have a variety of different ownership claims. TOS: "Journey to Babel" is a simple "Desilu production" under just the Desilu logo, while the later "A Piece of the Action" displays the Desilu logo, but a Paramount Pictures Corporation copyright.
- "Mirror, Mirror" was the first to be filmed after the late July ribbon-cutting on the Gulf+Western/Desilu merger, but no episode of the season began filming prior to the February merger announcement.
- Gene L. Coon remained the producer, but he was replaced mid-season by John Meredyth Lucas.
- D.C. Fontana, who took the position of story editor near the end of season one, remained in this capacity during the second season.
- However, after the departure of Rolland M. Brooks (the last episode he worked on was "Amok Time"), Walter M. Jefferies remained the series' sole art director.
- Most of the seasons' episodes were helmed by one of three prominent directors, Joseph Pevney, Marc Daniels and Ralph Senensky. Assistant director Gregg Peters was promoted to unit production manager.
- Andrea Weaver became the women's costumer for the series at the time "Catspaw" begins production. She would remain with the show throughout the remainder of the season and half of TOS Season 3.
- The first season and "Catspaw", "Metamorphosis", "Friday's Child", and "Amok Time" did not use a copyright until 1978 so starting with "Who Mourns for Adonais?", all of the episodes have the correct copyright date to them at the end of each episode.
- TOS Season 2 performers
- TOS Season 2 UK VHS
- TOS Season 2 DVD
- TOS-R Season 2 DVD
- TOS Season 2 Blu-ray
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