“Balance of Terror” features the first appearance on Star Trek of actor Mark Lenard, as the Romulan Commander. Lenard also portrayed Spock’s father, Sarek, in the TOS episode “Journey to Babel” (in addition to
Star Trek III: The Search for Spock,
Star Trek IV: The Voyage Home, & two episodes of TNG) as well as the Klingon captain in
Star Trek: The Motion Picture. Thus, Lenard was the first person to play Star Trek’s
three major alien races—Vulcan, Klingon, & Romulan.
“Balance of Terror” is the only episode of TOS to exhibit Kirk presiding over a wedding ceremony. “Balance of Terror” is also the only episode of TOS in
which Enterprise’s weapons are shown to be controlled from another room besides the bridge. Other episodes strongly imply that the helmsman has direct control
over the weapons.
“Balance of Terror” also features the sole appearance of Lieutenant Stiles at the navigator position almost exclusively manned by
Mr Chekov in later episodes. Mr Stiles hates Romulans & transfers his antipathy to Spock when he discovers that Vulcans look like Romulans.
The Romulan Bird of Prey is technologically superior to Enterprise in two respects: its cloaking device & its extremely powerful plasma torpedoes. However, the
Bird of Prey is technologically inferior to Enterprise in its lack of warp drive.
Several ST episodes & Star Trek: First Contact imply, suggest, or state that the Federation does not initiate
first contact unless a civilization is warp-capable. Interestingly, based on this criterion, the Romulans are not
eligible for first contact either at the time of “Balance of Terror” or 100 years earlier during the Earth-Romulan War.
The Organians introduced in “Errand of Mercy” are the fourth all-powerful energy beings featured in the first season of TOS alone. The others were the
Thasians of “Charlie X,” Trelane & his parents in “The Squire of Gothos,” & the Metrons of “Arena.” This was a major theme in Star
Trek: TOS & all subsequent Star Trek series (although the later series tended to limit these beings to the Q). However, the Organians are the first omnipotent
energy beings with whom Kirk & Spock interact throughout the episode instead of appearing at the end of the episode as a deus ex machina. Nevertheless,
the Organians do not reveal their true nature until the end of the episode & so are still a deus ex machina, albeit one that is slightly better explored & understood.
That the very first confrontation between the crew of the Star Trek: TOS Enterprise & the Federation’s most frequent opponent, the Klingon Empire, should
result in a peace treaty effectively tying the hands of both races through omnipotent & omniscient means is ironic.
Captain Koloth mentions the Orgainian Peace Treaty in “The Trouble with Tribbles” in an inter-episodic
reference rare in Star Trek: TOS.
The crew of Enterprise NX-01 of Star Trek: Enterprise encounters the Organians in “Observer Effect.”
“Tomorrow Is Yesterday” was the landmark, first episode of TOS in which the crew of Enterprise engage in time travel, albeit inadvertantly at first.
However, at the end of the episode, the crew intentionally slingshot the ship around the sun to achieve time travel, a method they would use again in the second-season
episode “Assignment: Earth” & Star Trek IV: The Voyage Home. Consequently, this is also the first
episode in which Kirk, Spock, & company struggle with the repercussions of changing history.
“Tomorrow Is Yesterday” accurately predicted not only the year of the first manned moon shot, 1969, but that the launch would take place on Wednesday!
In “Tomorrow Is Yesterday,” Kirk tells Captain Christopher that there are 12 ships like her (Enterprise) in the fleet. This is usually taken to mean that
Enterprise is one of 12 Constitution-class Starships in Starfleet at the time, but sometimes
that Enterprise is the thirteenth vessel in the inventory.
Since the Enterprise travels to the year 1968 in “Assignment: Earth” but to 1969 in “Tomorrow Is Yesterday,” the events of this first-season
episode actually transpire after the events of the second-season “Assignment: Earth” from the standpoint of Twentieth-Century Earth at any rate. Therefore,
the alien-trained, enhanced human agent called Gary Seven had already been on Earth for a year when Enterprise encounters Captain Christopher in “Tomorrow Is
Yesterday.” This situation is addressed in the second issue of the 2008 comic book mini-series Star Trek: Assignment: Earth written & pencilled by comics legend
John Byrne.