Balance of Terror (episode)
The Enterprise battles a Romulan ship suspected of destroying outposts near the Neutral Zone.

Summary

Teaser 

Captain James T. Kirk is officiating at a wedding between two crew members, Angela Martine and Robert Tomlinson, when suddenly a red alert klaxon interrupts the ceremony, followed by a request for Captain Kirk to report to the bridge. Kirk learns that Earth Outpost 4 is under attack as everyone runs to battle stations.

Act One
The  investigates in the vicinity of the Romulan Neutral Zone, where an unknown assailant is methodically destroying each of the Earth outposts bordering the Zone. Spock explains to the crew that the Neutral Zone was established after the Earth-Romulan War over a century ago. Neither race has had contact with the other since that time, and neither side knows what the other looks like. Kirk then tells the crew that while self-defense is permitted, they are forbidden by Starfleet Command's orders to violate the Neutral Zone. The Enterprise and its crew are to be considered expendable. 

Lieutenant  assumes the attacking vessel is Romulan, but Kirk points out that after a century, no one would know what a Romulan ship looks like. Stiles shares his knowledge of Romulan ship markings, as a number of his relatives died in the Earth-Romulan war. "Their war, Mr. Stiles," says Kirk. "Not yours."

Earth Outposts 2 and 3 are found to be destroyed, and the Enterprise briefly contacts Outpost 4. The sole survivor of Outpost 4, Commander Hansen, describes a powerful blast of energy from a ship they couldn't track and the destruction of Outpost 8. He then reports that the ship has reappeared. A view relayed from the outpost's sensors shows the ship firing, and then the viewing screen goes blank.

Spock's sensors detect a moving object, but nothing is visible on the screen. He suggests that the Romulans have some sort of invisibility shield. Since the Romulan ship seems to be in no hurry, Kirk theorizes that it may not be aware of the Enterprise. Spock then reports that the ship is heading back towards the Neutral Zone. 

Despite objections from Stiles, Kirk orders a parallel course instead of an intercept course. By matching the unknown ship's course and speed, he hopes to make the Enterprise seem like an echo. Under no circumstances is the Enterprise to enter the Romulan Neutral Zone without a direct order from Kirk. Stiles points out that there could be Romulan spies on board the Enterprise, and Sulu recommends maintaining a security alert.

Uhura picks up a communication signal, through which Spock is able obtain a view of the Romulan ship's interior, providing the Federation their first visuals of the Romulans. Stiles notices the Romulan captain's physical resemblance to Spock.

Act Two
As Uhura attempts to interpret the Romulan signals, Stiles sarcastically suggests giving the job to Spock. Kirk orders him to keep his bigotry to himself.

Meanwhile, on the bridge of the Romulan ship, the Romulan commander has noticed the Enterprise following them. He confers with one of his officers (the centurion) on the ethics of their mission. He then rebukes and demotes another officer, Decius, for dispatching a subspace message in violation of orders for radio silence. The centurion warns the commander that Decius has powerful friends. The commander quietly expresses distaste for the mission but assures the centurion of his devotion to his duty.

In the Enterprise briefing room, the officers discuss their chances against the Romulan ship. Spock demonstrates the effect of the Romulan weapon on Outpost 4's protective shields, and Scott reports that the Romulan ship's power is "simple impulse". Stiles urges an attack, arguing from history that running would guarantee war. Spock agrees, pointing out that Vulcan had begun to colonize space before giving up its warlike ways, and that if the Romulans are indeed descended from ancient Vulcans, they are more dangerous than Kirk might realize. After a moment, Kirk gives the order to attack. The Enterprise heads into battle at red alert.

Act Three

Following the Romulan ship's path towards a comet's tail, Kirk orders the Enterprise to jump forward and attack the Romulan ship when its trail becomes visible. The Romulan commander hopes to double back to intercept the Enterprise, but, on learning that his target is no longer following, orders an evasive maneuver. Each commander, having failed in his plans, reflects on the other's intelligence.

A barrage of phaser fire damages the Romulan ship. The centurion pushes the Romulan commander out of the way of falling debris but is fatally injured himself. Meanwhile, the phaser circuits on the Enterprise burn out as the Romulan ship fires its primary weapon. Kirk orders full astern and as the Enterprise backs up, they find that the weapon has a range limit which causes the shot to partially dissipate, resulting in reduced impact. 

Determined to prevent the Romulan ship from reentering the Neutral Zone, Kirk orders another barrage of phaser fire. Unable to stop the Romulan ship, and aware of the consequences, Kirk orders the Enterprise into the Neutral Zone. Displaying restrained emotion as his friend dies, the Romulan commander orders all debris and, sadly, the body of his friend into the escape chute as a decoy. The Enterprise picks up the debris on the sensors but in doing so, loses track of the Romulan ship.

Act Four

It has come down to a waiting game and both ships have powered down in the Neutral Zone to prevent detection. After the Enterprise has been powered down for 9 hours and 47 minutes, Kirk tries to rest in his quarters, when Yeoman Rand walks in and asks the captain if he would like something to eat from the galley. Kirk shakes his head and tells Rand to get him coffee and have it on the bridge, as he will be heading up there soon. Just then, Dr. McCoy arrives as Rand leaves. Kirk confesses that he wishes he were on a cruise somewhere with no responsibility. He admits to McCoy that when his crew looks to him to make the next move, he wonders, "What if I'm wrong?" McCoy struggles at first to come up with an answer to this and Kirk does not expect him to provide one. However, McCoy puts his hand on Kirk's shoulder and gently says, "In this galaxy, there's a mathematical probability of three million Earth-type planets. And in all the universe, three million million galaxies like this. And in all of that, and perhaps more, only one of each of us. Don't destroy the one named Kirk."

Later on the bridge, Spock, while making repairs, accidentally activates a panel, and the Romulan ship detects the Enterprise and moves in to attack. Kirk anticipates this and manages to fire on the Romulan ship. Furious, the Romulan commander orders more debris into the disposal tubes, including a nuclear warhead. 

Spock picks up the "metal-cased object" on his sensors and the Enterprise fires upon it. The massive explosion causes damage to the Enterprise but despite now having the upper hand, the Romulan commander decides to head for home. 

Scott reports that while phasers are operational, only Tomlinson, the groom from the wedding, is manning the station. Stiles quotes his experience with phasers and Kirk sends him down to assist. In an attempt to lure the Romulan ship back, the Enterprise plays dead.

Despite his reservations, and the crippled status of his ship, the Romulan commander is reminded by Decius that it is the commander's duty to crush the enemy. The commander then reluctantly gives the order to attack.

Meanwhile, Spock checks on the phaser crew and Stiles coldly remarks that they "will handle things without your help, Vulcan."  After Spock leaves however, a phaser coolant leak erupts. As the Romulan ship moves in to attack, Kirk gives the order to fire phasers. But both Tomlinson and Stiles have been overcome by the coolant fumes. Realizing the danger, Spock runs back and manages to fire the phasers in time, severely damaging the Romulan ship.

Visual contact between ships is somehow established as Kirk watches a severely wounded Romulan commander stagger to his feet. The Romulan commander turns and looks upon Kirk's face. Despite Kirk's offer to beam aboard any survivors, the Romulan commander informs him that it is not the Romulan way. He then says, with admiration, "I regret that we meet in this way. You and I are of a kind. In a different reality, I could have called you friend," and as the last part of his duty, he sets the Romulan ship to self-destruct. Kirk watches regretfully as the ship is destroyed.

Kirk goes to sickbay and discovers that not only did Spock fire the phasers, but he also rescued Stiles. Stiles is humbled and amazed that Spock saved his life after everything he had said to him. Unfortunately, Spock was unable to save Robert Tomlinson. Kirk is then forced to console his grief-stricken fiancée, Angela Martine, while she stands alone in the chapel. "It never makes any sense. We both have to know that there was a reason," Kirk says softly to Martine. She tearfully assures the captain that she will be fine and leaves.

Log entries
 Captain's log, USS Enterprise (NCC-1701), 2266

Memorable quotes 

"Since the days of the first wooden vessels, all ship masters have had one happy privilege: that of uniting two people in the bonds of matrimony."
- Kirk, in the chapel

"I had no idea that history was your specialty."
"Family history."
- Kirk and Stiles, on the Romulan War

"Their war, Mister Stiles. Not yours."
- Kirk, after Stiles lists his family losses in the Romulan War

"Happy wedding day, almost."
"You won't get off my hook this easily. I'm going to marry you, mister. Battle or phaser weapons notwithstanding."
- Tomlinson and Angela, in the phaser control room

"Leave any bigotry in your quarters. There's no room for it on the bridge."
- Kirk, to Stiles, after he implies that Spock could be a Romulan spy

"That Earth outpost sent word to an Earth vessel, now it follows."
"Which neither retreats nor grows near, which turns as we turn. Commander, it is our judgment that we run from a reflection."
"Perhaps so, but my judgment prevails."
- Romulan commander and Romulan bridge officer

"He has friends. And friends of his kind mean power. And power is danger."
"Danger and I are old companions."
- Romulan centurion and Romulan commander, after Decius is demoted in rank

"Not too soon for me to see the stars of home."
- Romulan commander, to the centurion

"War is never imperative, Mister Spock."
"It is for them, Doctor. Vulcan, like Earth, had its aggressive, colonizing period; savage, even by Earth standards. And if the Romulans retained this martial philosophy, then weakness is something we dare not show."
- McCoy and Spock, after the latter agrees with Stiles on attacking the Romulans

"I wish I were on a long sea voyage somewhere. Not too much deck tennis, no frantic dancing. And no responsibility."
- Kirk to McCoy, on the Romulan incursion

"In this galaxy, there's a mathematical probability of three million earth-type planets… and in all the universe, three million million galaxies like this one. And in all of that, and perhaps more, only one of each of us. Don't destroy the one named Kirk."
- McCoys advice to Kirk

"He's a sorcerer, that one! He reads the thoughts in my brain!"
- Romulan commander to Decius, on Kirk

"You and I are of a kind. In a different reality, I could have called you friend."
- Romulan commander to Kirk, after the Romulan ship is disabled

"We are creatures of duty, Captain. I have lived my life by it. Just one more duty to perform."
- Romulan commanders last words

"It never makes any sense. We both have to know that there was a reason."
- Kirk to Martine, on Tomlinson's death

 Background information
Production timeline
 Theatrical premiere of "The Enemy Below": 
 Theatrical premiere of "Run Silent, Run Deep": 
 Story outline by Paul Schneider: 
 Revised Story outline: , 
 First draft teleplay: 
 Second draft teleplay: 
 Revised teleplay by John D.F. Black: 
 Second revised teleplay by Black: 
 Final draft teleplay by Gene Roddenberry: 
 Revised final draft teleplay: 
 Additional revisions: , , , , 
 Filmed:  – 
 Day 1 – , Wednesday – Desilu Stage 9: Int. Bridge
 Day 2 – , Thursday – Desilu Stage 9: Int. Bridge
 Day 3 – , Friday – Desilu Stage 9: Int. Bridge
 Day 4 – , Monday – Desilu Stage 9: Int. Bridge, Chapel (redress of Transporter room), Phaser control room (redress of Engineering)
 Day 5 – , Tuesday – Desilu Stage 9: Int. Kirk's quarters, Briefing room, Sickbay, Corridors
 Day 6 – , Wednesday – Desilu Stage 9: Int. McCoy's office, Romulan bridge
 Day 7 – , Thursday (Half Day) – Desilu Stage 9: Int. Romulan bridge
 Original airdate: 
 Rerun date: 
 First UK airdate: 
 Remastered airdate: 

Story and script
 The plot of this episode is based on the 1957 film , with the Enterprise taking the part of the American destroyer and the Bird-of-Prey with its cloaking device taking the part of the submarine. (The Star Trek Compendium 4th ed., p. 40) Director Vincent McEveety had seen the film but only noticed the similarity later, when this was pointed out to him. He commented, "Obviously, it's the same story." (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 34)
 Star Trek: The Original Series 365 (p. 063) suggests that Schneider may have also been inspired by another submarine film, . The authors note that the film contains a similar plot thread of an officer longing for vengeance, as well as the tactic of releasing wreckage and bodies from a damaged vessel in order to mislead the opposing ship. The Star Trek Compendium (5th edition, p. 40) also mentions this film as the inspiration along with The Enemy Below.
 The "Revised Final Draft" of the script was disseminated on 18 July 1966. (Cover)
 A portion (scene 46) with the doomed Commander Hansen was filmed but cut from the final episode.  In it, Hansen informed Kirk that the Romulan vessel is of "starship design" and that the Romulans had probably stolen Earth designs via espionage and traitors. This is the basis for Stiles' remarks in scene 52 about a vessel "remarkably similar to ours" and having Romulan spies aboard the Enterprise, which was aired and before he even knew what Romulans looked like. 
 A shot filmed for scene 171 but cut from the finished episode shows Kirk saluting the Romulan commander, which the latter acknowledges with a courteous nod, before destroying his ship. 

Production
 The music featured during the opening scenes of the wedding ceremony is the 19th century English tune "Long, Long Ago."
 Although phasers are used throughout the episode, the visual effect seen is that which later was used for photon torpedo launches, probably because the term "photon torpedo" was not invented until later in the season, in . Kirk orders the phasers to be "set for proximity blast"; each phaser blast acts like a Navy depth charge.
This is the only time in the series that the Below decks Phaser weapons room is seen.
 The Making of Star Trek and The Star Trek Compendium (4th ed., p. 40) state that the ship's chapel was a redress of the transporter room. Inside Star Trek: The Real Story (pp. 170-171), states that it is, instead, a redress of the briefing room.
 The trailer includes footage of the Enterprise firing its phasers from  instead of the "blast-like" phaser effect seen in the actual episode.

Cast
 Regular first season extra Ron Veto gets his only close-up in TOS, when he replaces Stiles at the navigation console.
 Two of the actors playing Romulans in this episode later played Vulcan characters, namely Mark Lenard (Sarek) and Lawrence Montaigne (Stonn).

Costumes
 The Romulan helmets shown aboard the Romulan bridge were designed to cover the ears of the actors. This saved the additional cost of creating prosthetic ear-points for each of the supporting actors. They were reused in  (on Vulcans) and  for the same reason. (Star Trek: The Original Series 365, p. 173)
 The rarely seen command work utility jumpsuit is worn by several crew members in this episode.

Continuity
 This episode saw the introduction of the Romulan Star Empire in Star Trek. Paul Schneider is credited with creating the Romulans. Schneider remarked, "It was a matter of developing a good Romanesque set of admirable antagonists that were worthy of Kirk. I came up with the concept of the Romulans which was an extension of the Roman civilization to the point of space travel, and it turned out quite well." (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 34) Schneider's next contribution was .
Associate producer / story editor John D.F. Black said about Schneider, "He was the father of the Romulans. Not Gene, not me, not anyone else – but Paul Schneider. And when he came up with the Romulan characters, they were so wonderful – I mean, they were full. I liked that script a lot." (These Are the Voyages: TOS Season One, p. 217)
 "Balance of Terror" introduces cloaking devices to the Star Trek universe. While this episode suggests that they are a new development in interstellar history,  and  establish that Starfleet has encountered Suliban and Klingon cloaks in the past (2151 and 2256, respectively).
 This is the only time in which the ship's weaponry is fired through a chain of commands (Kirk, to Stiles, to phaser room), although  comes close with Bailey's phaser drills.
 When Kirk requests communication with the Romulan flagship, Uhura opens a hailing frequency from the navigation console, which seems unusual. However, when she left the communications station, Uhura had shut down most of the light indicators, which could indicate a transfer of functionality to the navigator's position. This is not the first time the navigation console has been used to open communications. In  and , when Captain Christopher Pike and Captain Kirk, respectively, want to "address intercraft," the system is opened from the navigation console. This apparently is also true in the alternate reality, because in ,  is able to address the crew of the  from his position at navigation.
 As an homage, Captain Picard's wedding remarks in  are almost the same as those Kirk uses. ()
 An alternate timeline version of the events of this episode is shown in , in which Christopher Pike remains captain of the Enterprise, while Kirk is present as captain of the .
 This episode contains the first mention of Romulus's neighboring planet Remus, which later appears prominently in .

Preview
The preview contains a Captain's Log recorded solely for the preview: "Captain's log, stardate 1710.0. The starship Enterprise is under heavy attack by an enemy vessel."

Reception
 McEveety recalled, "[Kirk and the Romulan commander] were very heroic characters pitted one against the other, and it dealt with the length to which people would go for their honor. It was a morality fantasy play, but terribly gripping. I thought that Mark Lenard's performance was brilliant, as was Bill Shatner's. It was a two-people show that I felt was real strong." (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 34)
 Mark Lenard said, "The Romulan Commander was one of the best roles I ever had on TV." Comparing the part with that of Sarek, Lenard elaborated, "In many ways, I did enjoy that role [Sarek], but I think the more demanding role and the better acting role was the Romulan Commander". (These Are the Voyages: TOS Season One, p. 217)
 Gene Roddenberry picked this as one of his ten favorite episodes for the franchise's 25th anniversary. (TV Guide, August 31, 1991)
 According to the original showrunner of , Bryan Fuller, the events of "Balance of Terror" were to provide a "touchstone" for the series.  However, since Fuller left the series during its development, it is unclear what exactly this was supposed to entail. The Romulans have not been seen or mentioned on Discovery thus far, though Romulus was mentioned in .
 In , Ted Sullivan described the Discovery episode  as "'Balance of Terror' good". 

Apocrypha
 In the James Blish adaptation of this story, presumably based on an earlier draft of the script, Stiles dies. In addition, Robert Tomlinson and Angela Martine actually marry, in a second ceremony late in the story. When the Enterprise fires on the Romulan ship for the final time, the latter explodes immediately, with the conversation between Kirk and the Romulan commander being omitted.
 In the William Shatner  The Return, where Kirk is resurrected by a Borg/Romulan alliance to kill Captain Jean-Luc Picard, the Romulan alliance is arranged by the granddaughter of the Romulan commander of this mission, convinced that Starfleet are brutal murderers and seeking revenge for her grandfather's death at Kirk's hands.
 The story of the events on Romulus leading up to this episode are told in the  "".
 A different background to this episode is told in the novella The First Peer and the novel Summon the Thunder, where Vrax is the Praetor who authorized the Neutral Zone incursion.
 In the novel Headlong Flight, an experiment in dimensional displacement results in the  of the "prime" universe – over a decade after  – encountering both an alternate version of the  – from a year after the Battle of Wolf 359, in a timeline which ended with the death of Picard/Locutus of Borg – and a trio of Romulan ships from this era, in a timeline where the Romulan ship depicted here apparently destroyed Kirk's Enterprise in the final showdown.

 Remastered information
 "Balance of Terror" was the first episode of the remastered version of The Original Series to air, though in some markets it was preceded by . It premiered in syndication on the weekend  and most notably featured  shots of the comet, Romulan plasma torpedo, and Bird-of-Prey, as well as of the Enterprise and Bird-of-Prey "adrift".The next remastered to air was .Video and DVD releases
 US CED VideoDisc release: 
 US LaserDisc release:  Original US Betamax/VHS release: 
 Original UK VHS release (two-episode tapes, CIC Video): Volume 5, catalog number VHR 2250, release date unknown Japan LaserDisc release: 
 US VHS release: 
 UK re-release (three-episode tapes, CIC Video): Volume 1.3, 
 As part of the US VHS collection Star Trek - The Greatest Battles: 
 As part of the UK VHS collection Star Trek - Greatest Battles: 
 Original US DVD release (single-disc): Volume 4, 
 As part of the TOS Season 1 DVD collection
 As part of the Star Trek: Fan Collective - Captain's Log DVD collection
 As part of the TOS Season 1 HD DVD collection
 As part of The Best of Star Trek: The Original Series DVD collection
 As part of the TOS Season 1 Blu-ray collection

Links and references
Starring
William Shatner as Capt. Kirk

 Also starring
Leonard Nimoy as Mr. Spock
Mark Lenard as a Romulan Commander

Co-starring
Paul Comi as 
Lawrence Montaigne as Decius

Featuring
DeForest Kelley as Dr. McCoy
Grace Lee Whitney as Yeoman Rand
George Takei as Sulu
James Doohan as Scott
Nichelle Nichols as Uhura
Stephen Mines as Tomlinson
Barbara Baldavin as Angela
Garry Walberg as Hansen
And
John Warburton as The Centurion

Uncredited co-stars
John Arndt as Fields
 William Blackburn as Hadley
Robert Chadwick as a Romulan scope operator
Frank da Vinci as Brent
Walt Davis as Romulan crewman 1
Vince Deadrick as Romulan crewman 2
Jeannie Malone as a yeoman
Sean Morgan as Brenner
Eddie Paskey as Leslie
Ron Veto as Harrison
 Unknown actors as
Bobby

Command crewman
Command crew woman 1
Command crew woman 2
Command lieutenant
Crewman 1
Crewman 2
Medical technician
Operations crewman
Wedding attendee 1
Wedding attendee 2
Wedding attendee 3

Stunts
 Vince Deadrick (double)
 Allen Jaffe (stunt)

Stand-ins
 William Blackburn as the stand-in for DeForest Kelley
 Frank da Vinci as the stand-in for Leonard Nimoy
 Jeannie Malone as the stand-in for Grace Lee Whitney
 Eddie Paskey as the stand-in for William Shatner

References
2156; 2160; ability; Achilles' heel; act of war; adversary; "all decks alert"; "all hands"; amen; analysis; answer; area; assignment; assumption; asteroid; atomic weapon; battle stations; battle status; bearing; best man; bigotry; bird-of-prey; blip; body; bonds of matrimony; book; "Bones"; brain; briefing room; campaign; candelabra; carelessness; ; centurion; century; chance; commander; channel; chapel; cloaking system; code; coffee; command base; Command base nearest to Neutral Zone; comet; comet tail; command order; composition; comrade; condition red; conduit; conscience; contact; control circuit; couch; Cryptography; customer; ; damage report; dancing; danger; death; debris; deck; decode; deflector shield; disposal tube; distance; dust; duty; Earth; Earth Outpost Station; Earth-Romulan War; emergency call; emergency warp; enemy; ; escape maneuver one; estimate (estimating); evasive maneuvers (aka evasive action); family history; face-to-face; feeling; flagship; friend; fuel; fuel reserve; "full astern"; Galaxy Quadrant YX-12-114; galley; green; hailing frequency; heading (aka course); "Here Comes the Bride" (aka "Bridal Chorus"); history; homeland; hour; Human; Icarus IV; idea; identification; impact; implosion; impulse; interception course; intruder; invisibility screen; iron; junior officer; lab; lateral power; lectern; light; magnitude; ; master; match; maximum warp; memory; metal; meter; mile; minute; Milky Way Galaxy; million; mission; mistake; mister; motion sensor; navigator; Neutral Zone Incursion; no quarter; nuclear warhead; obedience; object; "of course"; opinion; order; "out of reach"; outpost station; Outpost 1; Outpost 2; Outpost 3; Outpost 4; Outpost 5; Outpost 6; Outpost 7; Outpost 8; overload; parallel course; patrol; phaser control room (aka phaser room, phaser control); phaser coolant; phaser coolant seal; phaser crew; phaser weapon; philosophy; plasma; plasma torpedo; plastaform; playing dead; power consumption; praetor; Praetor's flagship; probability; proof; protective shield; proximity fuse; question; radiation burn; range; rank; rank reduction; reality; Remus; ; risk; rodinium; Romii; Romulan Star Empire; Romulans; Romulan Bird-of-Prey; Romulan Neutral Zone; Romulan praetor; Romulus system; Romulus; rule of silence; salute; savage; science; sea; second; Sector Z-6; security alert; sensor (sensing device); sensor probe; sensor range; services; session; shipmaster; sighting; signal for war; sneak attack; sorcerer; space recorder; Space Service; space vessel; specialist; speaker; spy; "stand by"; standby alert; standby crew; starboard; star sector;  (Captain);  (Commander);  (Commander); Stiles family; subject; subspace radio; superior officer; surrender; survivor; Table of Comets''; tactic; tactical report; tape; telepathy; television camera device; tennis; theory; thing; thought; transfer coil; Treaty of 2160; trick; velocity; victory; viewing screen; Visual communication; Vulcans; Vulcan (planet); Vulcan history; weapons control; weapons crew; wedding day; wooden vessel

Unreferenced material
bird; bull; chest pain; creature; ; a medicine; seat-harness; terrier

External links

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TOS episodes