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* ''Artificial Condition''. Twice when [[Literature/TheMurderbotDiaries Murderbot]] goes into action one of the men it is fighting accidentally kills another in the confusion. Then for a RuleOfThrees Murderbot uses their boss as a BulletproofHumanShield against gunfire from her own bodyguard.
* In ''Literature/ABrothersPrice'', Jerin threatens to shoot Cira while he's escaping. She barely manages to get past the gun; then she [[TheMole helps]].
* Discussed in ''Literature/ArkRoyal'', where the titular old-fashioned [[TheBattlestar armored carrier]]'s sensors are so bad that the automated [[PointDefenseless point-defense]] guns have a good chance of mistaking one of the carrier's own fighters for an enemy and shooting it down. Unfortunately, since the aliens' stealth systems are so good they can easily bypass a fighter screen to strike at the ship herself, the ship's CAG orders that at least one wing must always remain close to the carrier to protect it, despite the risk from the point-defense guns.
* In Creator/LoisMcMasterBujold's ''Literature/CaptainVorpatrilsAlliance'', Ivan explains they still use dog tags to identify soldiers because implants might betray them to their enemies.
* In Creator/CSLewis's ''Literature/TheSilverChair'', having killed [[spoiler:the Lady of the Green Kirtle]], they set out warily into her underground kingdom -- her subjects are setting off firecrackers, and they fear signals -- but once they capture one to question, [[spoiler:Rilian reveals that he killed "Her Ladyship", the subjects reveal they were under MindControl]], and matters are settled all around.
* In Creator/RobertEHoward's "Literature/BeyondTheBlackRiver" Franchise/ConanTheBarbarian talks to a Pict in his own language to trick him ashore so he can kill him and steal his boat -- to BringNewsBack of the Pictish attack.
* In ''Franchise/TheDarkTower'' series, Roland mentions that he and his best friend Cuthbert killed their friend Alain after mistaking him for an enemy scout.
* In one battle in ''Literature/TheDiamondThrone'', a force masquerading as Pandion Knights is attacked by a force of legitimate Pandions. As both sides would be in the same armor design, the legitimate Pandions wear colored armbands to identify friend from foe.
* Creator/TerryPratchett's ''Literature/{{Discworld}}'':
** Asked by a [[TheGuardsMustBeCrazy palace guard]] when Mort, channeling [[TheGrimReaper Death himself]], tries to enter.
--->'''Guard:''' Friend or foe?\\
'''Mort:''' Which would you prefer?\\
'''Guard:''' ...Pass, friend.
** In ''Literature/InterestingTimes'', the {{Magitek}} terracotta warriors springing up beneath [[BigBad Lord Hong's]] army causes the soldiers to flee... towards the armies of his rival Lords who only joined forces because 7 barbarians had taken over TheEmpire. The soldiers assume that they're being attacked by Lord Hong and start fighting. It's noted later that these fights actually killed more of the soldiers than the terracotta warriors.
** In ''Literature/{{Jingo}}'', while Vimes is having a talk with 71-hour Ahmed in Klatch, they are attacked by a random Ankh-Morpork patrol looking for Klatchians to fight.
** ''Literature/{{Night Watch|Discworld}}'' has a group of the old City Watch defending Sam Vimes, while another group of Watchmen (led by an escaped criminal) are trying to kill him. The friendlies happen to be passing a lilac bush, so they each break off a blossom and stick it on their helmets. This becomes [[UsefulNotes/ThePoppy a tradition in later years]], with the survivors of the battle [[DueToTheDead wearing the lilac]] every 25th of May.
* ''{{Literature/Doom}}'' begins in Afghanistan where Fox company is lost in a mist. The company sees shadowy figures moving around and Lt. Weems panics and orders the Marines to attack. Arlene, the company scout, has gotten in close and confirmed that the men are unarmed monks. Weems refuses to listen, Fly tries to punch him out but fails, and Fox guns down civilians in a fog.
* In Creator/JimButcher's Literature/TheDresdenFiles novel ''Literature/DeadBeat'', [[spoiler:GrandTheftMe]] makes this very difficult to figure out.
* In Creator/WenSpencer's ''Endless Blue'', Mikhail immediately deploys Reds to guard on the crash; when he is asked what if someone approaching was friendly, he says they will learn that they are ''not''. He tones down the orders shortly. An officer complains that they can not use IFF -- Identification Friend or Foe -- to recognize anyone, and Mikhail orders maintaining radio silence, which will keep anyone from finding them.
* Happens in accordance with [[TruthInTelevision historical incidents]] of friendly fire in Jeff Shaara's [[UsefulNotes/AmericanCivilWar Civil War]] novels, ''Literature/GodsAndGenerals'' and ''Literature/TheLastFullMeasure''. General "Stonewall" Jackson is shot in ''Gods'' by fidgety sentries and dies of complications. General Longstreet is shot in ''Measure'' right after worrying that one rebel unit's black uniforms make them look like Yankees, but he eventually recovers.
* At the end of ''A Good Clean Fight'' by Creator/DerekRobinson, a (British) SAS patrol is ordered to intercept the survivors of a German bomber that landed out in the desert. They do, and capture the crew. A (also British) fighter squadron has received the same orders, but when they reach the bomber they see that someone's been there before them. They follow the tire tracks -- and thoroughly strafe the SAS patrol and kill everyone they see. [[TruthInTelevision It happened]].
* Part of the formula of ''Literature/TheHardyBoys'' series has the heroes, at the climax, briefly mistaking TheCavalry for enemy reinforcements.
* In Creator/EdgarRiceBurroughs's ''[[Literature/JohnCarterOfMars The Gods of Mars]]'', John Carter, trying to escape, attacks the approaching jailor -- only to realize that it wasn't the jailor, it was his own son. Briefly, he even thought he had killed him.
* In Creator/EEDocSmith's ''[[Literature/{{Lensman}} Triplanetary]]'', in the Atlantis section, Phryges is held at gun-point by a woman while he is undercover -- and he realizes it's his childhood friend Kinnexa. She insists on his turning around so she can check for a scar to be sure it's him.
* In Creator/HBeamPiper's ''Lord Kalvan of Otherwhen'', Kalvan discusses {{battle cr|y}}ies to keep their forces from attacking each other. At the battle itself, some of their foes attack others on their side; after it, Kalvan talks with one prisoner, who indignantly declares that he had been shouting his battle cry at the top of his lungs.
* In Creator/PatriciaCWrede's ''Literature/MairelonTheMagician'', Kim is accosted as she comes out of the pub, and blacks his eye before she realizes it's Mairelon.
* In Creator/PoulAnderson's ''Literature/AMidsummerTempest'', trying to reach the royalist forces brings up great fears of this being a problem; Rupert thinks he should not try to cut his hair so he can prove who he is, quickly.
* In Creator/EdgarRiceBurroughs's ''Literature/TheMonsterMen'', Sing shoots at ships he takes for pirates, though he knows they might not be, because being taken by pirates is too horrible to risk.
* In L. Jagi Lamplighter's ''Literature/ProsperosDaughter'' trilogy, at one point, someone pursuing Miranda by boat suffers a fatal accident on rocks. Only later does she learn he was one of her brother's men, trying to warn her of something.
* ''A Sailor of Austria'' by John Biggins.
** Lt. Otto Prohaska receives orders to shell enemy forces in a small harbour that isn't even on his maps. He turns up at where he thinks is the enemy area and starts shelling it with the deck gun, doing only minor damage, when the lookout suddenly realises they're shelling their own troops, so they quickly submerge and get the hell out of there. Later Prohaska reads in a newspaper about how his submarine bravely attacked an enemy harbour, causing such massive damage that the cowardly enemy fled in terror. ''In the same paper'' is an article about the brave Austrian soldiers who sank an enemy submarine who opened fire on them while [[DressingAsTheEnemy treacherously flying the Austrian flag]].
** Later the German navy accuse him of torpedoing one of their mine-laying submarines that had gone missing, one that had his future brother-in-law serving on it as well. His fiancee doesn't hold it against him as accidents happen in war, and Otto is eventually cleared of the accusation, but he lives with this doubt for years until he finally comes across proof that the submarine blew itself up with a malfunctioning mine.
* In Creator/MichaelFlynn's ''[[Literature/SpiralArm In The Lion's Mouth]]'', a secret espionage war has friendly fire accidents: one man is killed by another on his side, because of his cover. Later, Dominic Tight is targetted [[spoiler:in an actual fight, where his invisibility cloak hides his identity.]]
* This happens in ''Franchise/StarWarsLegends'' novels as the Galactic Civil War progresses, particularly in works like the ''Literature/XWingSeries''. Due to VehicularTurnabout, the Rebels/New Republic end up using an increasing amount of Imperial military hardware, from captured Star Destroyers to [[MookMobile TIE Fighters]] (though in the latter case the Rebels try to put as many DeflectorShields on the starfighters as possible, along with painting large, bright red Rebel starbird emblems on the solar panels). So veteran pilots get to deal with lingering nervousness as they approach a friendly Star Destroyer, and in some battles squadron leaders have to tell their pilots not to take a snap-shot at any TIE until their targeting computer confirms it's an enemy. Wraith Squadron in particular, due to their success with TheInfiltration of enemy forces, has a few close calls when an X-Wing pilot sees the TIE in their crosshairs flip from a red to blue target.
* Franchise/TolkiensLegendarium:
** In ''Literature/TheChildrenOfHurin'', Túrin, having been captured by Orcs [[spoiler: mistakes his best friend Beleg, who has come to rescue him, for one of his captors and kills him]]. This triggers a major HeroicBSOD.
** In ''Literature/TheReturnOfTheKing'', the sight of the fleet causes panic in Gondor until its flag becomes clear.
* ''TabletopGame/Warhammer40000'' books:
** In Creator/JamesSwallow's Literature/BloodAngels novel ''Deus Encarmine'', many Blood Angels, driven into the Black Rage, fall blindly on each other -- an effect that the survivors [[HeroicBSOD actually admit]] [[LosingTheTeamSpirit frightened them]]. When they counter-attack and take down the enemy ship, the Word-Bearers' helots are driven mad by the psykers' deaths and fall on each other -- blocking the Word-Bearers' way, so they slaughter them, too.
** In Creator/SandyMitchell's Literature/CiaphasCain novel ''Death or Glory'', when he made vox contact with Sergeant Tayber, Tayber refused to give him his position because he didn't know he was really a commissar, and went to meet him instead; this gives Cain hope that he has hit on a competent officer. Later, Lieutenant Piers is about to open fire on their [[DressingAsTheEnemy orkish vehicles]], and when Cain hails them, still demands that he prove it.
** In Creator/DanAbnett's Literature/GauntsGhosts novel ''Only In Death'', in an apparently haunted stronghold, the Ghosts repeatedly bring up guns only to discover they were about to shoot their own men. No friendly fire occurs, although sometimes because another soldier stops it.
*** In ''Blood Pact'', Criid attacks a figure in the streets; he wrestles with her until he can point out that he's Gaunt.
** In Creator/GrahamMcNeill's Literature/HorusHeresy novel ''False Gods'', Davin's moon is so mist-bound that Loken is always bringing up his gun to shoot before he recognized an ally. More seriously, remembrancer Petronella Vivar takes it upon herself to go to the battlefield, and her shuttle goes unrecognized and is fired upon.
*** In Creator/JamesSwallow's ''The Flight of the Eisenstein'', Garro refuses to shoot on a Thunderbird without hailing it to find out why.
*** In Creator/GrahamMcNeill's ''Fulgrim'', Lucius [[spoiler:[[TurnCoat having betrayed them to Horus]], tricks Captain Demeter into helping him kill the loyalist Space Marines with him.]]
** In William King's ''Literature/SpaceWolf'', when Ragnar escapes the [[{{Mordor}} caves]], he faces a lot of guns in the hands of Space Marines. Although he thinks they recognize him, he is very, very, very careful, because it would be irony indeed to escape the Chaos Space Marines to die at the hands of friends.
*** In ''Grey Hunters'', they find soldiers, and Ragnar spies on them to discover that they are loyalist. He is very careful about contacting them, in order to avoid provoking a fight.
*** In Lee Lightner's ''Sons of Fenris'', when Ragnar is leading Space Wolves in the jungle, they reach the city, and find that the comms don't work, and they are taken for enemy. Ragnar has to charge through the attack to make contact. Later, when Ragnar [[TheNoseKnows smells]] that there are other Space Marines in the city, he and the rest of the Wolfblade ready for combat, just in case.
** In Creator/GrahamMcNeill's ''Storm of Iron'', the Chaos forces herd prisoners toward the Imperial outpost. They are slaughtered, and the forces learn the positions of the Imperial guns.
** In Creator/DanAbnett's ''Literature/{{Titanicus}}'', Cally Samstag had the troopers [[YouAreInCommandNow flee after one of them sent a message]]. They are still tracked down by skitarii. When they ask for them to GetItOverWith, the skitarii say they have sent for a rescue and then realizes that they thought it was an enemy.
** In Creator/GrahamMcNeill's Literature/{{Ultramarines}} novel ''Dead Sky, Black Sun'', after a fight, [[spoiler:the Unfleshed]] take Uriel and his companions prisoner because they might be friendly -- though they think probably not.
*** In ''The Killing Ground'', when the Space Marines make contact with Imperial forces, they first scout them carefully; Pasanius assures Uriel that their machinery is well-maintained, which points toward Imperial forces, but they still meet them with some trepidation, as there is no way to be sure. Later when the Grey Knights arrive, they take Uriel and Pasanius prisoner -- none too gently -- because they might be tainted and so enemies.
** In Andy Hoare's Literature/WhiteScars novel ''Hunt for Voldorius'', the Raven Guard, seeing someone arrive, discuss the possibilities -- not allies of the Chaos forces, since they arrived secretly, but they could be Chaos forces that are rivals, and they don't see any way they could be Imperial. It is fortunate that one White Scar scout made out some of the Raven Guard and voxed an abort to the Thunderbirds, and the Raven Guard intercepted it; there was nearly a fratricidal bloodbath.
* In Creator/LloydAlexander's ''[[Literature/{{Westmark}} The Kestrel]]'', a battle-mad Theo shoots a Regian soldier before he realizes it's actually his queen (and, to make it worse, his betrothed) DressingAsTheEnemy.
* At one point in ''Literature/TheWheelOfTime'' series, Rand's attempt to secure the allegiance of the [[ProudWarriorRace Aiel clans]] has caused a civil war among that race, and he has to put down the rebellious faction before they can lay waste to civilization. The Aiel on his side are convinced to wear armbands so that the non-Aiel forces know not to attack them; they take this as a great insult, as they can tell one clan from another at a glance from the cut of their clothing.
* In ''Literature/TheWinterWar'' by Antti Tuuri, many cases of confusion occur.
** A group of Russians walk right through the Finnish lines in the dark, thought to be tired and grumpy Finnish combat engineers when they don't answer the password challenge. The narrator thinks the Russians themselves were unaware of what happened and believed the Finns had already withdrawn further.
** A story is heard about a Finnish pilot who makes a forced landing between the lines and is fired at from both directions, and being wounded and confused, he himself can't tell where the friends are since there's a Swedish-speaking unit on the Finnish side.
* ''Harry's Game'' by Gerald Seymour involves an undercover agent being sent to infiltrate Belfast to catch an IRA gunman. He eventually catches his quarry and shoots him, only to be shot himself by a British army sniper (who from his point-of-view saw one civilian shoot another). The authorities issue a deliberately vague statement to make the press think it was a MutualKill instead.
* ''KG 200'' by J.D. Gilman and John Clive is about a Luftwaffe unit that specializes in flying captured Allied aircraft. It opens with an American bomber that's been fatally damaged by German flak, and it's only gradually revealed that the crew is German also and they were meant to be dropping spies over England. Later as word of the fake Allied planes gets out, the gunner on an Allied bomber shoots down another bomber that's behaving suspiciously. Turns out it really was a friendly, but their commanding officer pretends they made the right decision to preserve morale.
* In ''Literature/ABrothersPrice'', Jerin threatens to shoot Cira while he's escaping. She barely manages to get past the gun; then she [[TheMole helps]].
* Discussed in ''Literature/ArkRoyal'', where the titular old-fashioned [[TheBattlestar armored carrier]]'s sensors are so bad that the automated [[PointDefenseless point-defense]] guns have a good chance of mistaking one of the carrier's own fighters for an enemy and shooting it down. Unfortunately, since the aliens' stealth systems are so good they can easily bypass a fighter screen to strike at the ship herself, the ship's CAG orders that at least one wing must always remain close to the carrier to protect it, despite the risk from the point-defense guns.
* In Creator/LoisMcMasterBujold's ''Literature/CaptainVorpatrilsAlliance'', Ivan explains they still use dog tags to identify soldiers because implants might betray them to their enemies.
* In Creator/CSLewis's ''Literature/TheSilverChair'', having killed [[spoiler:the Lady of the Green Kirtle]], they set out warily into her underground kingdom -- her subjects are setting off firecrackers, and they fear signals -- but once they capture one to question, [[spoiler:Rilian reveals that he killed "Her Ladyship", the subjects reveal they were under MindControl]], and matters are settled all around.
* In Creator/RobertEHoward's "Literature/BeyondTheBlackRiver" Franchise/ConanTheBarbarian talks to a Pict in his own language to trick him ashore so he can kill him and steal his boat -- to BringNewsBack of the Pictish attack.
* In ''Franchise/TheDarkTower'' series, Roland mentions that he and his best friend Cuthbert killed their friend Alain after mistaking him for an enemy scout.
* In one battle in ''Literature/TheDiamondThrone'', a force masquerading as Pandion Knights is attacked by a force of legitimate Pandions. As both sides would be in the same armor design, the legitimate Pandions wear colored armbands to identify friend from foe.
* Creator/TerryPratchett's ''Literature/{{Discworld}}'':
** Asked by a [[TheGuardsMustBeCrazy palace guard]] when Mort, channeling [[TheGrimReaper Death himself]], tries to enter.
--->'''Guard:''' Friend or foe?\\
'''Mort:''' Which would you prefer?\\
'''Guard:''' ...Pass, friend.
** In ''Literature/InterestingTimes'', the {{Magitek}} terracotta warriors springing up beneath [[BigBad Lord Hong's]] army causes the soldiers to flee... towards the armies of his rival Lords who only joined forces because 7 barbarians had taken over TheEmpire. The soldiers assume that they're being attacked by Lord Hong and start fighting. It's noted later that these fights actually killed more of the soldiers than the terracotta warriors.
** In ''Literature/{{Jingo}}'', while Vimes is having a talk with 71-hour Ahmed in Klatch, they are attacked by a random Ankh-Morpork patrol looking for Klatchians to fight.
** ''Literature/{{Night Watch|Discworld}}'' has a group of the old City Watch defending Sam Vimes, while another group of Watchmen (led by an escaped criminal) are trying to kill him. The friendlies happen to be passing a lilac bush, so they each break off a blossom and stick it on their helmets. This becomes [[UsefulNotes/ThePoppy a tradition in later years]], with the survivors of the battle [[DueToTheDead wearing the lilac]] every 25th of May.
* ''{{Literature/Doom}}'' begins in Afghanistan where Fox company is lost in a mist. The company sees shadowy figures moving around and Lt. Weems panics and orders the Marines to attack. Arlene, the company scout, has gotten in close and confirmed that the men are unarmed monks. Weems refuses to listen, Fly tries to punch him out but fails, and Fox guns down civilians in a fog.
* In Creator/JimButcher's Literature/TheDresdenFiles novel ''Literature/DeadBeat'', [[spoiler:GrandTheftMe]] makes this very difficult to figure out.
* In Creator/WenSpencer's ''Endless Blue'', Mikhail immediately deploys Reds to guard on the crash; when he is asked what if someone approaching was friendly, he says they will learn that they are ''not''. He tones down the orders shortly. An officer complains that they can not use IFF -- Identification Friend or Foe -- to recognize anyone, and Mikhail orders maintaining radio silence, which will keep anyone from finding them.
* Happens in accordance with [[TruthInTelevision historical incidents]] of friendly fire in Jeff Shaara's [[UsefulNotes/AmericanCivilWar Civil War]] novels, ''Literature/GodsAndGenerals'' and ''Literature/TheLastFullMeasure''. General "Stonewall" Jackson is shot in ''Gods'' by fidgety sentries and dies of complications. General Longstreet is shot in ''Measure'' right after worrying that one rebel unit's black uniforms make them look like Yankees, but he eventually recovers.
* At the end of ''A Good Clean Fight'' by Creator/DerekRobinson, a (British) SAS patrol is ordered to intercept the survivors of a German bomber that landed out in the desert. They do, and capture the crew. A (also British) fighter squadron has received the same orders, but when they reach the bomber they see that someone's been there before them. They follow the tire tracks -- and thoroughly strafe the SAS patrol and kill everyone they see. [[TruthInTelevision It happened]].
* Part of the formula of ''Literature/TheHardyBoys'' series has the heroes, at the climax, briefly mistaking TheCavalry for enemy reinforcements.
* In Creator/EdgarRiceBurroughs's ''[[Literature/JohnCarterOfMars The Gods of Mars]]'', John Carter, trying to escape, attacks the approaching jailor -- only to realize that it wasn't the jailor, it was his own son. Briefly, he even thought he had killed him.
* In Creator/EEDocSmith's ''[[Literature/{{Lensman}} Triplanetary]]'', in the Atlantis section, Phryges is held at gun-point by a woman while he is undercover -- and he realizes it's his childhood friend Kinnexa. She insists on his turning around so she can check for a scar to be sure it's him.
* In Creator/HBeamPiper's ''Lord Kalvan of Otherwhen'', Kalvan discusses {{battle cr|y}}ies to keep their forces from attacking each other. At the battle itself, some of their foes attack others on their side; after it, Kalvan talks with one prisoner, who indignantly declares that he had been shouting his battle cry at the top of his lungs.
* In Creator/PatriciaCWrede's ''Literature/MairelonTheMagician'', Kim is accosted as she comes out of the pub, and blacks his eye before she realizes it's Mairelon.
* In Creator/PoulAnderson's ''Literature/AMidsummerTempest'', trying to reach the royalist forces brings up great fears of this being a problem; Rupert thinks he should not try to cut his hair so he can prove who he is, quickly.
* In Creator/EdgarRiceBurroughs's ''Literature/TheMonsterMen'', Sing shoots at ships he takes for pirates, though he knows they might not be, because being taken by pirates is too horrible to risk.
* In L. Jagi Lamplighter's ''Literature/ProsperosDaughter'' trilogy, at one point, someone pursuing Miranda by boat suffers a fatal accident on rocks. Only later does she learn he was one of her brother's men, trying to warn her of something.
* ''A Sailor of Austria'' by John Biggins.
** Lt. Otto Prohaska receives orders to shell enemy forces in a small harbour that isn't even on his maps. He turns up at where he thinks is the enemy area and starts shelling it with the deck gun, doing only minor damage, when the lookout suddenly realises they're shelling their own troops, so they quickly submerge and get the hell out of there. Later Prohaska reads in a newspaper about how his submarine bravely attacked an enemy harbour, causing such massive damage that the cowardly enemy fled in terror. ''In the same paper'' is an article about the brave Austrian soldiers who sank an enemy submarine who opened fire on them while [[DressingAsTheEnemy treacherously flying the Austrian flag]].
** Later the German navy accuse him of torpedoing one of their mine-laying submarines that had gone missing, one that had his future brother-in-law serving on it as well. His fiancee doesn't hold it against him as accidents happen in war, and Otto is eventually cleared of the accusation, but he lives with this doubt for years until he finally comes across proof that the submarine blew itself up with a malfunctioning mine.
* In Creator/MichaelFlynn's ''[[Literature/SpiralArm In The Lion's Mouth]]'', a secret espionage war has friendly fire accidents: one man is killed by another on his side, because of his cover. Later, Dominic Tight is targetted [[spoiler:in an actual fight, where his invisibility cloak hides his identity.]]
* This happens in ''Franchise/StarWarsLegends'' novels as the Galactic Civil War progresses, particularly in works like the ''Literature/XWingSeries''. Due to VehicularTurnabout, the Rebels/New Republic end up using an increasing amount of Imperial military hardware, from captured Star Destroyers to [[MookMobile TIE Fighters]] (though in the latter case the Rebels try to put as many DeflectorShields on the starfighters as possible, along with painting large, bright red Rebel starbird emblems on the solar panels). So veteran pilots get to deal with lingering nervousness as they approach a friendly Star Destroyer, and in some battles squadron leaders have to tell their pilots not to take a snap-shot at any TIE until their targeting computer confirms it's an enemy. Wraith Squadron in particular, due to their success with TheInfiltration of enemy forces, has a few close calls when an X-Wing pilot sees the TIE in their crosshairs flip from a red to blue target.
* Franchise/TolkiensLegendarium:
** In ''Literature/TheChildrenOfHurin'', Túrin, having been captured by Orcs [[spoiler: mistakes his best friend Beleg, who has come to rescue him, for one of his captors and kills him]]. This triggers a major HeroicBSOD.
** In ''Literature/TheReturnOfTheKing'', the sight of the fleet causes panic in Gondor until its flag becomes clear.
* ''TabletopGame/Warhammer40000'' books:
** In Creator/JamesSwallow's Literature/BloodAngels novel ''Deus Encarmine'', many Blood Angels, driven into the Black Rage, fall blindly on each other -- an effect that the survivors [[HeroicBSOD actually admit]] [[LosingTheTeamSpirit frightened them]]. When they counter-attack and take down the enemy ship, the Word-Bearers' helots are driven mad by the psykers' deaths and fall on each other -- blocking the Word-Bearers' way, so they slaughter them, too.
** In Creator/SandyMitchell's Literature/CiaphasCain novel ''Death or Glory'', when he made vox contact with Sergeant Tayber, Tayber refused to give him his position because he didn't know he was really a commissar, and went to meet him instead; this gives Cain hope that he has hit on a competent officer. Later, Lieutenant Piers is about to open fire on their [[DressingAsTheEnemy orkish vehicles]], and when Cain hails them, still demands that he prove it.
** In Creator/DanAbnett's Literature/GauntsGhosts novel ''Only In Death'', in an apparently haunted stronghold, the Ghosts repeatedly bring up guns only to discover they were about to shoot their own men. No friendly fire occurs, although sometimes because another soldier stops it.
*** In ''Blood Pact'', Criid attacks a figure in the streets; he wrestles with her until he can point out that he's Gaunt.
** In Creator/GrahamMcNeill's Literature/HorusHeresy novel ''False Gods'', Davin's moon is so mist-bound that Loken is always bringing up his gun to shoot before he recognized an ally. More seriously, remembrancer Petronella Vivar takes it upon herself to go to the battlefield, and her shuttle goes unrecognized and is fired upon.
*** In Creator/JamesSwallow's ''The Flight of the Eisenstein'', Garro refuses to shoot on a Thunderbird without hailing it to find out why.
*** In Creator/GrahamMcNeill's ''Fulgrim'', Lucius [[spoiler:[[TurnCoat having betrayed them to Horus]], tricks Captain Demeter into helping him kill the loyalist Space Marines with him.]]
** In William King's ''Literature/SpaceWolf'', when Ragnar escapes the [[{{Mordor}} caves]], he faces a lot of guns in the hands of Space Marines. Although he thinks they recognize him, he is very, very, very careful, because it would be irony indeed to escape the Chaos Space Marines to die at the hands of friends.
*** In ''Grey Hunters'', they find soldiers, and Ragnar spies on them to discover that they are loyalist. He is very careful about contacting them, in order to avoid provoking a fight.
*** In Lee Lightner's ''Sons of Fenris'', when Ragnar is leading Space Wolves in the jungle, they reach the city, and find that the comms don't work, and they are taken for enemy. Ragnar has to charge through the attack to make contact. Later, when Ragnar [[TheNoseKnows smells]] that there are other Space Marines in the city, he and the rest of the Wolfblade ready for combat, just in case.
** In Creator/GrahamMcNeill's ''Storm of Iron'', the Chaos forces herd prisoners toward the Imperial outpost. They are slaughtered, and the forces learn the positions of the Imperial guns.
** In Creator/DanAbnett's ''Literature/{{Titanicus}}'', Cally Samstag had the troopers [[YouAreInCommandNow flee after one of them sent a message]]. They are still tracked down by skitarii. When they ask for them to GetItOverWith, the skitarii say they have sent for a rescue and then realizes that they thought it was an enemy.
** In Creator/GrahamMcNeill's Literature/{{Ultramarines}} novel ''Dead Sky, Black Sun'', after a fight, [[spoiler:the Unfleshed]] take Uriel and his companions prisoner because they might be friendly -- though they think probably not.
*** In ''The Killing Ground'', when the Space Marines make contact with Imperial forces, they first scout them carefully; Pasanius assures Uriel that their machinery is well-maintained, which points toward Imperial forces, but they still meet them with some trepidation, as there is no way to be sure. Later when the Grey Knights arrive, they take Uriel and Pasanius prisoner -- none too gently -- because they might be tainted and so enemies.
** In Andy Hoare's Literature/WhiteScars novel ''Hunt for Voldorius'', the Raven Guard, seeing someone arrive, discuss the possibilities -- not allies of the Chaos forces, since they arrived secretly, but they could be Chaos forces that are rivals, and they don't see any way they could be Imperial. It is fortunate that one White Scar scout made out some of the Raven Guard and voxed an abort to the Thunderbirds, and the Raven Guard intercepted it; there was nearly a fratricidal bloodbath.
* In Creator/LloydAlexander's ''[[Literature/{{Westmark}} The Kestrel]]'', a battle-mad Theo shoots a Regian soldier before he realizes it's actually his queen (and, to make it worse, his betrothed) DressingAsTheEnemy.
* At one point in ''Literature/TheWheelOfTime'' series, Rand's attempt to secure the allegiance of the [[ProudWarriorRace Aiel clans]] has caused a civil war among that race, and he has to put down the rebellious faction before they can lay waste to civilization. The Aiel on his side are convinced to wear armbands so that the non-Aiel forces know not to attack them; they take this as a great insult, as they can tell one clan from another at a glance from the cut of their clothing.
* In ''Literature/TheWinterWar'' by Antti Tuuri, many cases of confusion occur.
** A group of Russians walk right through the Finnish lines in the dark, thought to be tired and grumpy Finnish combat engineers when they don't answer the password challenge. The narrator thinks the Russians themselves were unaware of what happened and believed the Finns had already withdrawn further.
** A story is heard about a Finnish pilot who makes a forced landing between the lines and is fired at from both directions, and being wounded and confused, he himself can't tell where the friends are since there's a Swedish-speaking unit on the Finnish side.
* ''Harry's Game'' by Gerald Seymour involves an undercover agent being sent to infiltrate Belfast to catch an IRA gunman. He eventually catches his quarry and shoots him, only to be shot himself by a British army sniper (who from his point-of-view saw one civilian shoot another). The authorities issue a deliberately vague statement to make the press think it was a MutualKill instead.
* ''KG 200'' by J.D. Gilman and John Clive is about a Luftwaffe unit that specializes in flying captured Allied aircraft. It opens with an American bomber that's been fatally damaged by German flak, and it's only gradually revealed that the crew is German also and they were meant to be dropping spies over England. Later as word of the fake Allied planes gets out, the gunner on an Allied bomber shoots down another bomber that's behaving suspiciously. Turns out it really was a friendly, but their commanding officer pretends they made the right decision to preserve morale.
