->''"Idiots! What good's a guided missile if it comes right back?"''
-->-- '''Androsa Pilot''', ''[[VideoGame/StarFoxZero Star Fox Zero: The Battle Begins]]''

A guided missile has been launched [[BusFullOfInnocents at an orphanage]] or one of the protagonists' planes, usually once it's been damaged and left limping along with no anti-missile defenses. Those onboard can't escape and get a nice, long look at their oncoming doom as they say their prayers... till the AcePilot flies his plane in front of the missile, making it switch targets and leading it away.

The AcePilot either has the skills to blow it up or a plan (well, [[IndyPloy more like on the spot improvising]]) to destroy or escape from the missile. Usually by [[HighSpeedMissileDodge deftly dodging]] [[WronskiFeint and making it hit a cliff or asteroid]], just plain letting it hit his plane but using an EjectionSeat beforehand, or best of all, [[StopHittingYourself leading it back to the launcher!]] If he's being chased by the MacrossMissileMassacre, then expect his new target to go "OhCrap"

Needless to say, the missile ''will not'' have any Friend Or Foe recognition software to tell it to either dodge the ally plane or not explode.

This can very easily turn into a HeroicSacrifice if he can't destroy or evade it, or worse ram an enemy target to make sure both he and the missile hit it. Compare GrenadeTag.



[[folder:Anime & Manga]]
* Mao does [[http://www.youtube.com/watch?v=ixpnrbWvsa8&t=10m20s this]] to protect a helicopter full of refugees in the first episode of ''LightNovel/FullMetalPanic The Second Raid''. Of course, it was justified that her AS is custom-equipped with electronic warfare equipment. Plus the fact that she did this with ARF missiles which also exist in real life; according to Wiki/TheOtherWiki, they are specifically built in a way that if someone attempts to jam them, they lock onto the jammer instead(!).
* The ''Manga/BlackLagoon'' crew divert heat seeking missiles with a flare, before [[CrazyAwesome launching their boat in the air and taking the attacking helicopter down with a torpedo]].
* In ''Manga/YuYuHakusho'', Yusuke escapes several explosive homing shuriken by accidentally misguiding them in this way.
* Subverted in ''Manga/DragonBallZ'' when Frieza chases Goku around with razor-sharp guided energy disks. Goku has the idea to do this and trick Frieza into cutting himself. Frieza sees through it immediately and demonstrates sufficient skill controlling the disks as to avoid endangering himself. [[spoiler:Then double-subverted when Goku distracts Frieza enough that one of the disks bisects him from behind anyway.]]
* Charles does this in ''Anime/ToaruHikushiENoTsuioku'' when up against a patrol of Amatsukami airships.
* In ''Manga/Area88'' Shin does this when he is bounced by [[spoiler:a pair of [=MiG=]s while in an unarmed Phantom.]]

[[folder:Films -- Animation]]
* Used to introduce us to most of the titular dog's powers in the intro to Disney's ''Disney/{{Bolt}}'', Bolt grabs a magnetic landmine, and unintentionally gets a homing missile on his tail, which he runs away from, leading it back toward a different helicopter which he jumps over, but the missile hits home.
* ''WesternAnimation/TheManCalledFlintstone'' has Fred and Barney reprogram the missile and then trick the villains inside the missile as it flies off into deep space.

[[folder:Films -- Live-Action]]
* In ''Film/AirForceOne'', a RedShirt F-15 pilot deliberately flies into a missile to save the heroes.
** Which makes the RedShirt a jet fighter pilot secret service agent, taking one for the President.
* ''Film/TheIncredibleMrLimpet''. A wolf pack of Nazi submarines has fired torpedoes at an Allied convoy. The title character discovers that the torpedoes have been modified to follow his "thrum" (the booming call he can make). He uses this to make the torpedoes follow him away from the ships and hit the U-boats that fired them.
* ''Film/TheHuntForRedOctober'':
** Marko Ramius, the Soviet's submarine captain equivalent of an AcePilot; and Bart Mancuso, his American counterpart both do this with a ''ballistic missile submarine'', defeating not one but two torpedoes fired by a lurking "[[ReportingNames Alfa]]"-class. [[ArbitraryMinimumRange Ramius charges the first torpedo, reducing its run to less than its safety arming setpoint and resulting in a dud]]; when the Alfa's captain orders all safeties off the second torpedo, Mancuso leads the torp back toward the boat that fired it.
--> '''Alfa sonar officer:''' [[OhCrap Torpedo dead ahead!]]\\
'''Alfa XO:''' You arrogant ass! [[HoistByHisOwnPetard You've killed us!]]
** The second torpedo actually gets misguided ''twice''; a few minutes earlier it has the ''October'' cold until the more maneuverable ''Dallas'' interposes itself then crash-surfaces to get away.
** There is also the time Ramius dodges a plane-dropped torpedo by making a sharp turn just before hitting a rock, causing the torpedo to be momentarily confused due to the bubbles.
* In ''Film/Godzilla1998'', Godzilla pulls a similar sub trick by guiding two torpedoes into one of the subs that fired them.
* Frankie in ''Film/SkyCaptainAndTheWorldOfTomorrow'', who leads an underwater crab robot's torpedo away and ejects when she can't blow it up. Sky Captain uses the crabs same torpedoes to destroy it by leading them back to it.
* ''Franchise/StarWars Episode II Film/AttackOfTheClones'' Obi Wan ejects the spare parts for Jango Fett's missile to hit.
** In ''Film/RevengeOfTheSith'' Anakin makes two missiles following him hit each other by spinning his fighter around.
* Pulled off by Topper in the finale of ''Film/HotShots''
* ''Film/GalaxyQuest''
-->'''Sarris:''' You fool! You fail to realize that, with your armor gone, my ship will tear through yours like tissue paper!\\
'''Jason Nesmith:''' And what ''you'' fail to realize is that [[spoiler: my ship is ''dragging mines!'']]
* In a variation on the theme, a Tomahawk missile is launched at an ArmsFair in the PreTitlesSequence of ''Film/TomorrowNeverDies''. ''After'' it's fired, Film/JamesBond manages to communicate that one of the planes there is armed with a nuclear torpedo, and if the Tomahawk blows ''that'' up it will make the fallout from Chernobyl look like spring rain. When the Royal Navy are unable to self-destruct the inbound Tomahawk, he nicks the plane.
* ''Payday'', the movie version of ''Series/DerClown'', shows [[AcePilot Dobbs]] as he sends a heat-seeking surface-to-air missile chasing his helicopter back into the SAM which is so glowing hot that it must emit more heat than the helicopter's gas turbines.
* In ''Film/BlueThunder'', this trope is inverted, in that the protagonist's helicopter is the intended target of heat-seeking missiles fired at him by Air Force interceptors, but he manages to decoy them away using the heat from, respectively, a Chinese barbecue shop and the sunlight reflecting off of a skyscraper. How this manages to avoid killing anyone is [[NoEndorHolocaust rather blatantly ignored]].
* The hero of ''Film/{{Interceptor}}'' pulls this at the end to shoot down the bad guy's stealth fighter, despite being unarmed.
* In ''Film/TheDarkKnightRises'', Batman manages to trick one of the missiles launched by one of the stolen Tumblers into blowing up one of the others after leading it on a long chase in the Bat.

* In the ''Literature/WingCommander'' novel ''End Run'', the Hornet squadron commander [[HeroicSacrifice sacrifices her fighter]] to take out a torpedo targeting the TCS ''Tarawa''.
* ''Franchise/StarWars'':
** Deliberately set up in ''Rogue Squadron'', the first book of the ''ComicBook/XWingSeries''. A ''Lancer'' frigate, specially designed to destroy fighters, has just appeared in the picture. Y-wings (slow bombers) can't get close enough for a missile lock without being vaped. The plan is going to be "let the X-wings distract the frigate so the Y-wings can escape," which is suicide. So Corran Horn comes up with a plan:
-->'''Corran''': "The Y-wings will be targeting the X-wing's homing beacon. Time it right, put the ''Lancer'' between the missiles and the X-wing, and you can scratch one ''Lancer''."
** Does not work as planed: some Y-Wings launch late and miss the frigate as it broke in half from the impacts (CMOA?) and come after Corran for real. He is lucky that his astromech shuts down the homing beacon.
** Mara Jade in [[Literature/NewJediOrder ''Destiny's Way'']] fighting some [[ScaryDogmaticAliens Yuuzhan Vong]] in a submarine pulls off a [[HighSpeedMissileDodge High Speed Torpedo Dodge]] then guides the torpedo right back at them.
* The Creator/DaleBrown book ''Shadow Command'' has a demonstration of the Black Stallion SpacePlane's superiority over older planes by having one trick a pair of Russian missiles into destroying the planes they were fired from.
* ''Literature/RedStormRising'':
** Inverted in the first Backfire raid on the NATO carrier battle group. Soviet target training missiles launched by TU-16 Badgers decoy US Navy aircraft away from their carrier group, instead of aircraft leading away missiles.
** Also played straight in the novel, where the anti-sub helicopters of the HMS ''Battleaxe'' and USS ''Reuben James'' play "decoy" to lure away anti-ship missiles from their respective ships, after it was determined that the Soviets were focusing on the escorts to make the job easier for other Soviet forces to get at the convoys the escorts were defending.
** And also played straight with the NATO convoys in general, with the use of chaff to decoy missiles away from ships. The problem was that a missile that had flown through a chaff cloud would then attempt to reacquire the closest target in the field of view of its seeker head, which was often -- if the geometry was right -- another ship. This is TruthInTelevision, by the way: at least one Royal Fleet Auxiliary ship in the UsefulNotes/FalklandsWar may have been lost this way.
* In Creator/TomClancy's ''[[Literature/JackRyan Executive Orders]]'', the Chinese purposefully incite an incident with Taiwan by using this as an excuse. A Chinese pilot fires a missile at a jetliner, then claim the Taiwanese are the ones that did it. Unfortunately, they didn't realize that US intelligence capabilities were so good, allowing the Americans to point out several discrepancies with the incident, and ultimately resulting in the formal recognition of Taiwan as a legitimate country.
* Stewart Cowley's ''Terran Trade Authority'' universe - Gerling, the commander of the human forces in the Laguna Wars, reminisces about how he earned his seniority: the missiles of the assault ships in the Terran battlefleet had entered a decay cycle which would result in their unavoidable premature detonation. Unwilling simply to fire them off into the wild black yonder where they might hit unwary ships, he orders a half-built ship to be towed into orbit to act as the sacrificial target.
* In ''Literature/HaloTheFallOfReach'', Jacob Keyes's UNSC ''Iroquois'' evades a Covenant destroyer's plasma torpedo but it comes back around. So Keyes charges the destroyer, banking away at the last second, and the torpedo hits the ship and knocks out its shields, letting Keyes finish it off with a salvo of Archer missiles (which are otherwise all but useless against Covenant ships). This maneuver, the "Keyes Loop", helps win the battle and earns Keyes a promotion to captain.

[[folder:Live-Action TV]]
* ''Series/{{Battlestar Galactica|2003}}'':
** Twice in the miniseries, Apollo leads a missile away from ''Colonial One'', saving the president. Later, Starbuck does the same for Apollo.
** Averted in Season 4 premiere: There are simply [[MacrossMissileMassacre too many missiles]] and while they manage to shoot down the one heading for ''Colonial One'', ''Zephyr'', ''Astral Queen'' and a few others do end up getting hit.
* Done more than once on ''Series/{{JAG}}''. [[spoiler:Commander Rabb put himself in front of a "dirty nuke" missile, launched from a diesel-powered submarine and aimed at a Carrier Battle Group, after it closed too close to be shot down to lead it away until it's fuel ran out.]] And in a separate instance: [[spoiler:A similar trick was done with a torpedo, drawing it into one submarine to save another.]]
* This is basically the entire plot of the ''Series/StarTrekVoyager'' episode "Dreadnought": a sentient missile with a [[WeaponOfMassDestruction massive anti-matter warhead]] is convinced an inhabited planet is its authorised target. Captain Janeway is willing to fly ''Voyager'' into its path, but fortunately Torres is able to deactivate the weapon in time. The plot was repeated in "Warhead"; this time the crew were able to convince one of the (literally "smart") weapons to blow up the other missiles and avert a war.

[[folder:Tabletop Games]]
* A specialized version of this in ''TabletopGame/{{BattleTech}}'' are the so-called "Nemesis pods" available as ammunition to improved Narc launchers. Unlike regular homing pods, which help ''friendly'' missiles with matching guidance systems find the target they attach to, a Nemesis pod misdirects ''enemy'' missiles into hitting a "marked" unit belonging to their own side if that unit just so happens to conveniently stumble into their line of fire.

[[folder:Video Games]]
* In the endgame cutscene for ''VideoGame/{{Unreal}}: Return to Na Pali'', Prisoner 849 leads the Bodega Bay's missile back to it, crippling the ship and disabling its ability to pursue her shuttle.
* In another ''VideoGame/WingCommander'' example, "Maniac" has a nervous breakdown when a heatseeking missile he fired at a [[CatFolk Kilrathi]] fighter misses, and hits a Confed transport instead, assisting the kats in destroying it.
* Captain Jack "Heartbreak One" Bartlett took the missile away from Kei "Edge" Nagase's tail in the ''second'' mission of ''VideoGame/AceCombat5TheUnsungWar''. [[spoiler: Bartlett got shot down and it isn't until the end of the game you get to see him again]]
** Additionally, it is possible for the player to send an enemy missile back at an enemy this way. However, this results in a miss or player death about 19 out of 20 attempts on ground targets, 4 our of 5 attempts on water targets, and 99 out of 100 attempts on flying targets.
** In a later mission in Ace Combat 5, Nagase does the same thing with a SAM that was targeting you. She ejects in time, and the next mission is to rescue her.
* It's possible to do this with the boss Duon's missiles in ''VideoGame/SuperSmashBrosBrawl''.
* ''[[VideoGame/TheLegendOfZeldaOracleGames The Legend of Zelda: Oracle of Ages]]'' uses an interesting variant of this trope: the boss of the 7th dungeon is vulnerable only to its own projectile attacks. However, rather than luring them back to it (they aren't homing projectiles), you have to use the Long Hook to swap places with the big jellyfish and put it into the path of its own attack.
* Flash game [[http://www.newgrounds.com/portal/view/477976 Dodge]]. Missiles simply fly towards the player, and you get to hit the enemy with them.
* The entire first section of [[TrueFinalBoss The Doomsday Zone]] in ''[[VideoGame/Sonic3AndKnuckles Sonic & Knuckles/Sonic 3 & Knuckles]]'' consists of you doing this to Robotnik's ship with the homing missiles he fires at you.
* This is how you defeat Megaleg in ''VideoGame/SuperMarioGalaxy'', by blowing out the HumongousMecha with its own Bullet Bills.
** And for the giant robot Megahammer in ''VideoGame/SuperMarioGalaxy2'', where you have to eat its own Bullet Bills with Yoshi and shoot them back at certain points on the robot.
* In ''VideoGame/SwordOfTheStars'', destroyers equipped with the Wild Weasel mission section can spoof enemy missiles into tracking it instead of the more valuable targets. Later patches/addons added the chance of some of these missiles returning "to sender" for a nasty surprise. In the latter case, the firing ship's [[PointDefenseless point-defense]] weapons will not intercept the returning missiles. The dreadnought Electronic Warfare command section does this along with two other important functions (sensor jamming and long-range scanning).
* In VideoGame/{{Portal}}, turret-launched missiles, though not true homing projectiles, can be sent wherever you please with cleverly-placed portals. This strategy is essential for the final boss.
* In the ComicBook/Marvel2099 sections of ''VideoGame/SpiderManShatteredDimensions'', it's possible to do this with the homing missiles fired by [[LawEnforcementInc Public Eye officers]]. You need to use [[BulletTime Accelerated Vision]], though.
* The purpose of the Target Override Pod in ''Tom Clancy's VideoGame/{{HAWX}}'' is to lock onto a friendly plane. If a missile starts tailing that plane, the Pod will redirect the missile at the Pod-equipped plane. Then it's all up to the Pod-equipped plane's pilot if the stunt ends up in TakingTheBullet or a HighSpeedMissileDodge.
* The final mission of the first ''VideoGame/MedalOfHonor'' has you sabotage a V2 rocket's guidance gyroscope, then launch it to destroy the base.
* Homing weapons in the ''VideoGame/EscapeVelocity'' series may lock onto the originating ship if jammed, provided that weapon has a particular Boolean flag turned on in its wëap resource. The games don't feature any examples, but the modders have added them.
* Played for laughs in ''VideoGame/SpyFox in Dry Cereal''. When you fix a crashed jet's circuit board, you're able to launch a missile that initially zooms off in a random direction, and we hear SPY Fox say, "I guess that guided missile was misguided." Then it flies back, crashing into a metal door it was initially aimed at, and then he says, "Of course, I planned that. I like a dramatic pause."
* This is how you "beat" (Annoy so much he sends away all the allies he's using to attack you) the Mad Dummy in {{VideoGame/Undertale}}.
* The old text-based computer game ''Hunt the Wumpus'' had crooked arrows (so that they could turn corners - don't think too much about it) which could go through 5 rooms and which you had to guide after shooting by typing the room number the arrow was to go to next, but if there was no passage from the room the arrow was in to the room you told it to go into, the arrow would "hit the wall" and expend the rest of its moves flying randomly. If it entered your room, it would hit you.
* ''VideoGame/FromTheDepths'': Typically an accidental event caused by a player forgetting to include an Identify Friend or Foe system in their missile systems design.
* In the ''VideoGame/StarFoxZero'' animated short "The Battle Begins" the pilot of the Androsa boss launches a volley of guided missiles at Fox's Arwing. Fox manages to dodge and shoot down three of the missiles before boosting ahead of the last one. He then manages to trick that missile into destroying Androsa's main laser canon by flying past it while it's firing.
** While largely impractical, this strategy can be re-enacted in the actual game, complete with the boss reacting the same way.
* ''VideoGame/MassEffectAndromeda'': Ryder uses such a tactic when attacking the kett armada at Meridian. While they have plenty of hacked Remnant warships backing them up, the kett still outgun them. So Ryder has the Remnant fly very close to the Scourge, that bizarre dark energy NegativeSpaceWedgie that homes in on Remnant technology, and thereby guides the Scourge tendrils to the kett ships and rips them apart. This works quite well and opens a hole for the ''Tempest'' to break through.

[[folder:Web Comics]]
* The ''Star Wars Episode III'' example (See Film above) is parodied by ''Webcomic/DarthsAndDroids'' [[http://www.darthsanddroids.net/episodes/0422.html here]]. With sentient missiles. Not intelligent; just sentient.

[[folder:Western Animation]]
* Done in ''WesternAnimation/{{Futurama}}''. With a burning flag. The episode was {{anvilicious}} about flag [[strike: burning]] ''eating''.
* In ''WesternAnimation/StarWarsCloneWars'', Anakin tells his clonetrooper pilots to fire all their missiles across the bow of the destroyer he's flying past. About half of the missiles destroy the droid starfighters pursuing Anakin; the other half start following Anakin, who then leads them into the open hangar of the Confederacy carrier.
* In the ''WesternAnimation/StarWarsTheCloneWars'' (not to be confused with the above series) episode "Cat and Mouse", Anakin defeats Separatist [[TheDreaded Admiral Trench]] - who has a history of taking out cloaked starships by having missiles lock onto their magnetic signature -- by provoking the Admiral into firing another round of missiles at his [[CallForward unusually]] [[Film/TheEmpireStrikesBack small]] stealth ship, redistributes the ship's power for maximum engine speed and luring the missiles right into the command bridge of Trench's dreadnought while its shields are still recharging and defenseless. As Anakin's ship speeds right towards the bridge, [[OhCrap Trench figures out too late exactly what he's trying to do]] and tries to get the shield back up in vain.
* Done with absolutely no logic in a ''WesternAnimation/SecretSquirrel'' short, where Secret for some reason possesses a "Fire away then turn around and blow myself up missile."
* In ''WesternAnimation/TaleSpin'', Baloo takes on an army of pandas in a fleet of hot air balloons armed with crude heat-seeking missiles by cramming his airplane full of ice cream (he had received large quantities of ice cream prior in the episode), causing the missiles to seek out the hot air in the pandas' balloons instead of the plane. This strategy, of course, meant he had to force the pandas to surrender or retreat before the ice cream melted.
* In ''WesternAnimation/DextersLaboratory'', Santa Claus defends his sleigh from Dexter's homing missiles by throwing several presents at it, causing the missile to hit the gifts instead and explode harmlessly in the sky. Unfortunately for Dexter, these happened to be his sister Dee Dee's presents.

[[folder:Real Life]]
* In the Falklands War, this was the job of a number of RN pilots in Sea King helicopters- including Prince Andrew.
* During the 2nd Indo-Pakistanese War (1973), an Indian [=MiG=] fired a missile at a Pakistani Mirage IIIE, but the missile shot down the [=MiG=]'s wingman.
** Similar incidents were recorded during the First Gulf War. Iraqi pilots were apparently given to the habit of taping their fire buttons down and a couple killed their own flight leaders this way.
* Naval history has recorded a number of incidents of ships managing to torpedo themselves due to malfunctions, a phenomenon called a "circular run".
** In 1879 the Peruvian ironclad ''Huascar'' tried to torpedo the Chilean corvette ''Abtao''. The torpedo went straight for 100 yards, then suddenly turned to port and circled back to ''Huascar''. Luckily for them, a crew member, Lt. Diaz Canseco, jumped overboard and shoved the torpedo to make it miss. Admiral Miguel Grau Seminario subsequently buried his remaining torpedoes in a cemetery.
** During UsefulNotes/WorldWarI, the cruiser USS ''Vesuvius'' was struck by a torpedo she launched during a weapons test, due to the aforementioned "swimming in a circle" issue. Due to some swift DamageControl, ''Vesuvius'' was saved from sinking due to this. It is with good reason that American torpedoes through some time in UsefulNotes/WorldWarII have a reputation as [[ReliablyUnreliableGuns being rather unreliable or possibly dangerous to their users]].
** UsefulNotes/WorldWarII:
*** The [[http://en.wikipedia.org/wiki/Mark_14_torpedo American Mark 14 Torpedo]] was notorious for running in circles, among other serious problems. There is only one confirmed case of a circular run sinking the submarine that launched it (the legendary USS ''Tang''), but there are several of circular-running torpedoes that either passed over a frantically crash-diving submarine or went off close by thanks to their deeply-problematic magnetic influence detonator. Even when they ran straight, Mk14s often ran too deep, failed to explode, or exploded prematurely, doing no damage to the enemy but loudly announcing the presence of an American submarine to any destroyer within 25 miles.
*** The cruiser HMS ''Trinidad'' was on convoy duty to the Soviet Union in the Arctic when it engaged three German destroyers. Two of its torpedo tubes froze up completely, and the third had the torpedo itself freeze in the water, causing it to hit ''Trinidad'' amidships. She managed to make it to Murmansk and be partially repaired, but an air attack on the way back started a fire that led to her being scuttled.
** A similar fate could have been suffered by a number of German U-boats, such as ''[[https://en.wikipedia.org/wiki/German_submarine_U-377 U-377]]'' and ''[[https://en.wikipedia.org/wiki/German_submarine_U-869 U-869]]''.
** One of the theories about the loss of the USS ''Scorpion'', an attack submarine, was that one of its torpedoes malfunctioned and accidentally turned on in the torpedo room, so it had to be fired off. However, it is thought that the guidance wires got cut when this happened, so it started looking for a target--and the only submarine in the area was the ''Scorpion'' itself. This theory is heavily disputed, however, and most torpedomen familiar with the Mark 37 torpedo deny that this could have happened given the failsafes of the design. Other theories suggest a major mechanical failure or hostile action by a nearby Soviet task force. The only thing that is certain is that both the US and Russian governments know more about what really happened than they will ever admit.
* Japanese pilot Sakio Komatsu earned himself a place in both Japanese and US history books when he intercepted one of six Mark 14 torpedoes fired by USS ''Albacore'' at his carrier, the ''Taihou'', with his own aircraft. He might not have gotten credit for it except for the fact that several hundred people saw it happen; it wasn't until about 1950 that US interrogators were actually satisfied it was true. This would turn out to be a ShaggyDogStory anyway. Of the 5 remaining torpedoes, 4 missed, and the last one hit the carrier and ruptured a tank of aviation-grade gasoline for the carrier's aircraft. The fumes from the gasoline later ignited and the resultant explosion sunk the carrier.
* Most missiles and torpedoes ''do not'' have IFF systems or methods to safe the weapon once it has been launched, so that the enemy can't render them useless via a compromised code. This is why most air-to-air missiles will detonate if they lose lock; it prevents them from engaging the wrong target, and gives them a slim chance, if they lost it due to evasion, of damaging the original.
* One of the major reasons why US submarines have almost exclusively trained and operated alone from the Cold War on is because if you lose the guidance wires, the torpedo will target anything that happens to cross its sonar's field of view.