Star Trek is an American science-fiction television series created by Gene Roddenberry that follows the adventures of the starship USS Enterprise (NCC-1701) and its crew. It is often referred to as Star Trek: The Original Series (TOS) to distinguish the show within the media franchise that it began.

The show is set in the Milky Way galaxy, roughly during the 2260s. The ship and crew are led by Captain James T. Kirk (William Shatner), First Officer and Science Officer Spock (Leonard Nimoy), and Chief Medical Officer Leonard ‘Bones’ McCoy (DeForest Kelley).

Shatner’s voice-over introduction during each episode’s opening credits stated the starship’s purpose:

Space: the final frontier.

These are the voyages of the starship Enterprise.

Its five-year mission: to explore strange new worlds, to seek out new life and new civilisations, to boldly go where no man has gone before.

Star Trek aired on NBC from September 8, 1966, to June 3, 1969. Star Trek’s Nielsen ratings while on NBC were low, and the network cancelled it after three seasons and 79 episodes. Several years later, the series became a hit in broadcast syndication, remaining so throughout the 1970s, achieving cult classic status and a developing influence on popular culture. Star Trek eventually spawned a franchise, consisting of eight television series, 13 feature films, and numerous books, games, and toys, and is now widely considered one of the most popular and influential television series of all time. The series contains significant elements of Space Western, as described by Roddenberry and the general audience.

Source: Wikipedia

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The majority of Star Trek episodes were first broadcast in the UK on BBC 1 between 1969 and 1973 and all episodes were broadcast out of order. The first run of episodes – all from Season 1 – was on Saturday evenings between July 12 and December 27, 1969 and was replaced in the schedules by Doctor Who (Season 7). Four episodes from the first season were not aired during the first run: “The Enemy Within” (aired during the second run), “Miri“(aired during the second run), “The Alternative Factor“, and “Operation: Annihilate!“(aired during the second run).

The second run began on Monday, April 6, 1970 with a repeat of “Court Martial“, followed by “The Enemy Within“. The run began broadcasts of Season 2 episodes and was interrupted for a month, after the broadcast of “A Piece of the Action” on September 7, 1970, re-starting on October 7, 1970 – moving from Monday to Wednesday nights. There was a break of three weeks between October and November 1970, beginning with “Assignment: Earth“, followed by a repeat of “Mirror, Mirror” before resuming episodes from Season 2. “The Doomsday Machine” was not included in the run. Season 1’s “Miri” and “Operation: Annihilate!” were broadcast in December 1970. Some Season 3 episodes were broadcast between December 16, 1970 (“The Empath” was scheduled for this date but was cancelled by the BBC) and February 10, 1971, immediately followed by selected repeats from Season 1 until April 14, 1971.

A third run of episodes began on Wednesday, September 15, 1971, resuming Season 3. These episodes appear to have been repeated on each following Sunday (except “Spock’s Brain” and the repeat of “This Side of Paradise“?) until December 19, 1971. The last ever Star Trek episode, “Turnabout Intruder” was broadcast on December 15, 1971 and this was followed by more selective repeats until July 5, 1972. The re-run of “What Are Little Girls Made Of?” was repeated on a Monday (December 27, 1971). “The Doomsday Machine” was finally broadcast on January 5, 1972.” The Doomsday Machine” and “Errand of Mercy” were repeated on Fridays (January 7 & 14, 1972, respectively, when these extra showings ceased).

There were a number of episodes from Season 3 that did not make it into the BBC’s original run. “The Paradise Syndrome” did not debut until April 16, 1973. “Plato’s Stepchildren” and “Whom Gods Destroy” were banned for the same reasons as “Miri” and “The Empath“, and were not broadcast until December 22, 1993 and May 22, 1998, respectively.

Star Trek episodes have been often repeated on BBC 1 and BBC 2 ever since.

Source: BBC Genome

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Episodes (original broadcast order)

Season 1

Where No Man Has Gone Before
(Broadcast July 12, 1969)
Season 1, Episode 3 of Star Trek. First repeated on February 17, 1971.

The Naked Time
(Broadcast July 19, 1969)
Season 1, Episode 4 of Star Trek. First repeated on February 9, 1972.

The City on the Edge of Forever
(Broadcast July 26, 1969)
Season 1, Episode 28 of Star Trek. First repeated on January 19, 1972.

A Taste of Armageddon
(Broadcast August 2, 1969)
Season 1, Episode 23 of Star Trek. First repeated on February 24, 1971.

Mudd’s Women
(Broadcast August 9, 1969)
Season 1, Episode 6 of Star Trek. First repeated on March 3, 1971.

Tomorrow is Yesterday
(Broadcast August 16, 1969)
Season 1, Episode 19 of Star Trek. First repeated March 10, 1971.

The Menagerie, Part 1
(Broadcast August 23, 1969)
Season 1, Episode 11 of Star Trek. First repeated January 26, 1972.

The Menagerie, Part 2
(Broadcast August 30, 1969)
Season 1, Episode 12 of Star Trek. First repeated on February 2, 1972.

The Devil in the Dark
(Broadcast September 6, 1969)
Season 1, Episode 25 of Star Trek. First repeated on March 17, 1971.

Charlie X
(Broadcast September 13, 1969)
Season 1, Episode 2 of Star Trek. First repeated on February 16, 1972.

Shore Leave
(Broadcast September 20, 1969)
Season 1, Episode 15 of Star Trek. First repeated on March 24, 1971.

Space Seed
(Broadcast September 27, 1969)
Season 1, Episode 22 of Star Trek. First repeated on March 31, 1971.

The Man Trap
(Broadcast October 4, 1969)
Season 1, Episode 1 of Star Trek. First repeated on February 23, 1972.

Dagger of the Mind
(Broadcast October 11, 1969)
Season 1, Episode 9 of Star Trek. First repeated on April 2, 1973.

The Corbomite Manoeuvre
(Broadcast October 18, 1969)
Season 1, Episode 10 of Star Trek. First repeated on April 7, 1971.

Balance of Terror
(Broadcast October 25, 1969)
Season 1, Episode 14 of Star Trek. First repeated on March 1, 1972.

The Squire of Gothos
(Broadcast November 1, 1969)
Season 1, Episode 17 of Star Trek. First repeated on April 14, 1971.

What are Little Girls Made Of?
(Broadcast November 8, 1969)
Season 1, Episode 7 of Star Trek. First repeated on December 22, 1971.

Arena
(Broadcast November 15, 1969)
Season 1, Episode 18 of Star Trek. First repeated on March 8, 1972.

The Return of the Archons
(Broadcast November 22, 1969)
Season 1, Episode 21 of Star Trek. This episode was not repeated until July 19, 1976.

This Side of Paradise
(Broadcast November 29, 1969)
Season 1, Episode 24 of Star Trek. First repeated on December 29, 1971.

Court Martial
(Broadcast December 6, 1969)
Season 1, Episode 20 of Star Trek. First repeated on April 6, 1970.

Errand of Mercy
(Broadcast December 13, 1969)
Season 1, Episode 26 of Star Trek. First repeated on January 12, 1972.

The Conscience of the King
(Broadcast December 20, 1969)
Season 1, Episode 13 of Star Trek. First repeated on March 15, 1972.

The Galileo Seven
(Broadcast December 27, 1969)
Season 1, Episode 16 of Star Trek. First repeated on March 22, 1972.

The Enemy Within
Broadcast April 13, 1970
Season 1, Episode 5 of Star Trek.

“Miri” (Season 1, episode 8) was not broadcast until December 2, 1970.

“The Alternative Factor” (Season 1, episode 27) was not broadcast until December 8, 1971.

“Operation: Annihilate!” (Season 1, episode 29) was not broadcast until December 9, 1970.

Season 2

Catspaw
Broadcast April 20, 1970
Season 2, Episode 7 of Star Trek.

Who Mourns for Adonais?
Broadcast April 27, 1970
Season 2, Episode 2 of Star Trek.

The Apple
Broadcast May 4, 1970
Season 2, Episode 5 of Star Trek.

Metamorphosis
Broadcast May 11, 1970
Season 2, Episode 9 of Star Trek.

Wolf in the Fold
Broadcast May 18, 1970
Season 2, Episode 14 of Star Trek.

The Changeling
Broadcast May 25, 1970
Season 2, Episode 3 of Star Trek2.

The Trouble with Tribbles
Broadcast June 1, 1970
Season 2, Episode 15 of Star Trek.

Bread and Circuses
Broadcast June 8, 1970
Season 2, Episode 25 of Star Trek.

Mirror, Mirror
Broadcast June 15, 1970
Season 2, Episode 4 of Star Trek.

Journey to Babel
Broadcast June 22, 1970
Season 2, Episode 10 of Star Trek.

The Deadly Years
Broadcast June 29, 1970
Season 2, Episode 12 of Star Trek.

A Private Little War
Broadcast July 6, 1970
Season 2, Episode 19 of Star Trek.

Obsession
Broadcast July 13, 1970
Season 2, Episode 13 of Star Trek.

By Any Other Name
Broadcast July 20, 1970
Season 2, Episode 22 of Star Trek.

I, Mudd
Broadcast July 27, 1970
Season 2, Episode 8 of Star Trek.

Patterns of Force
Broadcast August 3, 1970
Season 2, Episode 21 of Star Trek3.

The Immunity Syndrome
Broadcast August 10, 1970
Season 2, Episode 18 of Star Trek.

Return to Tomorrow
Broadcast August 17, 1970
Season 2, Episode 20 of Star Trek.

The Omega Glory
Broadcast August 24, 1970
Season 2, Episode 23 of Star Trek.

A Piece of the Action
Broadcast September 7, 1970
Season 2, Episode 17 of Star Trek.

The Ultimate Computer
Broadcast October 7, 1970
Season 2, Episode 24 of Star Trek.

Friday’s Child
Broadcast October 14, 1970
Season 2, Episode 11 of Star Trek.

Assignment: Earth
Broadcast November 4, 1970
Season 2, Episode 26 of Star Trek.

The Gamesters of Triskelion
Broadcast November 18, 1970
Season 2, Episode 16 of Star Trek.

Amok Time
Broadcast November 25, 1970
Season 2, episode 1 of Star Trek.

“The Doomsday Machine” (Season 2, episode 6) was not broadcast until January 5, 1972.

Miri
Broadcast December 2, 1970
Season 1, Episode 8 of Star Trek. This episode was effectively banned by the BBC after letters of complaint about its content. It was not repeated until October 14, 1992.

Operation: Annihilate!
Broadcast December 9, 1970
Season 1, Episode 29 of Star Trek.

“The Empath” (Season 2, episode 6) was scheduled for broadcast December 16, 1970. However, due to the outcry caused by “Miri“, the BBC chose not to screen this episode. It was not broadcast until January 5, 1994.

Season 3

Requiem for Methuselah
Broadcast December 30, 1970
Season 3, Episode 19 of Star Trek.

All Our Yesterdays
(Broadcast January 6, 1971)
Season 3, Episode 23 of Star Trek. First repeated on May 4, 1973.

Day of the Dove
(Broadcast January 13, 1971)
Season 2, Episode 7 of Star Trek. First repeated on May 11, 1973.

The Way to Eden
(Broadcast January 20, 1971)
Season 3, Episode 20 of Star Trek. First repeated on May 18, 1973.

Let That Be Your Last Battlefield
(Broadcast January 27, 1971)
Season 3, Episode 15 of Star Trek. First repeated on May 25, 1973.

Wink of an Eye
(Broadcast February 3, 1971)
Season 3, Episode 11 of Star Trek. First repeated on June 1, 1973.

The Cloud Minders
(Broadcast February 10, 1971)
Season 3, Episode 21 of Star Trek. First repeated on June 8, 1973.

Spectre of the Gun
(Broadcast September 15, 1971)
Season 3, Episode 6 of Star Trek. First repeated on June 15, 1973.

Elaan of Troyius
(Broadcast September 22, 1971)
Season 3, Episode 13 of Star Trek. First repeated on June 22, 1973.

The Enterprise Incident
(Broadcast September 29, 1971)
Season 3, Episode 2 of Star Trek. First repeated on June 29, 1973.

And the Children Shall Lead
(Broadcast October 6, 1971)
Season 3, Episode 4 of Star Trek. First repeated on July 5, 1973.

Spock’s Brain
(Broadcast October 13, 1971)
Season 3, episode 1 of Star Trek. First repeated on July 13, 1973.

Is There in Truth No Beauty?
(Broadcast October 20, 1971)
Season 3, episode 5 of Star Trek. First repeated on July 20, 1973.

For the World is Hollow and I Have Touched the Sky
(Broadcast October 27, 1971)
Season 3, episode 8 of Star Trek. First repeated on July 27, 1973.

That Which Survives
(Broadcast November 3, 1971)
Season 3, episode 17 of Star Trek. First repeated on August 3, 1973.

The Mark of Gideon
(Broadcast November 10, 1971)
Season 3, episode 16 of Star Trek. First repeated on August 10, 1973.

The Lights of Zetar
(Broadcast November 17, 1971)
Season 3, episode 18 of Star Trek. First repeated on August 17, 1973.

The Savage Curtain
(Broadcast November 24, 1971)
Season 3, episode 22 of Star Trek. First repeated on August 24, 1973.

The Tholian Web
(Broadcast December 1, 1971)
Season 3, episode 9 of Star Trek. First repeated on August 31, 1973.

The Alternative Factor
(Broadcast December 8, 1971)
Season 1, episode 27 of Star Trek. First repeated on September 10, 1973.

Turnabout Intruder
(Broadcast December 15, 1971)
Season 3, episode 24 of Star Trek. First repeated on September 17, 1973.

The Doomsday Machine
(Broadcast December 5, 1972)
Season 2, episode 6 of Star Trek. First repeated on August 7, 1974.

The Paradise Syndrome
(Broadcast April 16, 1973)
Season 3, episode 3 of Star Trek. First repeated on December 26, 1975.

Plato’s Stepchildren
(Broadcast December 22, 1993)
Season 3, episode 10 of Star Trek. Following complaints about “Miri“, this episode was effectively banned by the BBC due to its content until December 1993. First repeated on April 24, 1998.

The Empath
(Broadcast January 5, 1994)
Season 3, Episode 12 of Star Trek. Originally scheduled for broadcast on December 16, 1970, and following complaints about “Miri“, this episode was effectively banned by the BBC due to its content until January 1994. First repeated on May 8, 1998.

Whom Gods Destroy
(Broadcast May 22, 1998)
Season 3, episode 14 of Star Trek. Following complaints about “Miri“, this episode was effectively banned by the BBC due to its content until May 1998. First repeated on July 21, 2007.