Radar Is Useless

"No one who watches the skies for a living notices this [highly conspicuous aerial activity]." *ding*

— CinemaSins

Since its invention in the 1930s, radar (RAdio Detection And Ranging) has become a ubiquitous technology, used to ensure aeroplanes don't crash into each other, to predict the weather and track storms, and as the sensors your car uses to make annoying beeping noises when you're reversing too close to something. But its initial purpose was military, and indeed it remains a crucial part of modern warfare, with air-defence radar systems able to detect targets hundreds or even thousands of kilometres away. As such, it's no surprise that many billions of dollars have been spent on developing 'stealth' technologies to reduce planes' radar signature, and inversely, radars specifically designed to defeat these countermeasures.

But in fiction none of this matters, as in some cases even nigh-omnipotent ancient races can only produce detection systems roughly as effective as a partially-sighted old man with a pair of shoddy binoculars. Because of this, aircraft and spacecraft with no justification (such as a Cloaking Device or other forms of Stealth in Space) for avoiding detection are still able to get the drop on enemies in situations where they, realistically, should have seen it coming. Dropships are always able to penetrate deep into fortified enemy territory for infiltration missions, national militaries often seem worryingly oblivious to aerial combat going on in protected airspace, and nobody ever notices the massive alien attack fleet before flying saucers start blasting chunks out of cities. Those falling victim to this trope don't need to be explicitly shown to possess radar or some other form of detection system, just well-resourced and technologically advanced enough that it would be very likely for them to.

Of course, Tropes Are Tools: if basic detection systems actually worked in movieland as well as they do in our world, many Masquerades would be Broken (or at the very least The Men in Black would be forced to work overtime), and plots would never unfurl as they do if the heroes were unable to parachute onto the villain's island lair without being blasted out of the sky by AA guns.

If the radar itself is working perfectly, but the operators are too lazy and/or stupid to notice anything amiss, that's because it's manned by a Surveillance Station Slacker or The Guards Must Be Crazy.

Compare Swiss-Cheese Security, Insecurity Camera, The Radio Dies First and Cell Phones Are Useless, for other cases when technology fails to work and/or exist for plot-related reasons, as well as Failed a Spot Check, for extreme obliviousness at individual scale. Frequently overlaps with Militaries Are Useless when the heroes are left alone to fight a blatantly obvious airborne menace. Closely related to the endurance of the Old-School Dogfight as the most common form of aerial combat.

Radar systems which are are poorly made, obsolete or simply faulty don't count, hence No Real Life Examples, Please!

Has nothing to do with Getting Crap Past the Radar or a certain character from M*A*S*H.

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Examples:

Anime and Manga

• Cowboy Bebop: Subverted in "Jamming with Edward", which features a satellite equipped with artificial intelligence that controls a planet-threatening laser defense system. Spike tries to approach this advanced machine in an armed spacecraft just by turning his computer off and flying manually, guessing that its sensors are designed to detect the presence of active computers... But the satellite did see him approaching and dodged the attack.
• Both enforced and subverted in the Gundam franchise, as the Minovsky Particle (and similar super-science in other-universe works like Ahab Reactors in Iron Blooded Orphans) diffuses radar and radio waves — which is of course a justification for why Humongous Mecha have a practical military application in the setting. However, radar being interfered with by Minovsky particles is a dead giveaway that large military vehicles are nearby, even if it's much less precise. This is why the Shoal Zones (i.e. debris fields left over from battlefields and destroyed space colonies) are such popular hiding spots: there so much residual Minovsky interference (e.g. from wrecked ships still emitting Minovsky Particles) that it's easy to hide in them.
• One-Punch Man: The inability of any of the Hero Association's equipment across the globe to detect God is used as an immediate indicator of the staggering power gap that exists between him and the Hero Association.

Film — Live-Action

• The A-Team severely abuses this midway through the film: An air battle takes place between the A-Team in a stolen C-130 and two Reaper drones (which is impossible to begin with but that's beside the point), and Lynch sends an AC-130 gunship to attempt to kill the A-Team, yet all of this takes place in German airspace with no apparent reaction from the Bundeswehr.
• Armageddon (1998): An asteroid the size of Texas somehow goes undetected until it is less than two weeks away from striking Earth, due to debris destroying a Space Shuttle and bombarding New York, and even then an amateur astronomer has to show NASA where to look. Astronomers started hunting for space objects large enough to pose a threat several years before this film came out, and while they have missed incoming meteorites since (the 2013 Chelyabinsk meteor went completely unnoticed until it hit the atmosphere because it came from an angle close to the Sun), the stated size of the rock would make it bigger than Ceres (which was detected with an optical telescope all the way back in 1801) and therefore almost unmissable.
• Furious 7: The film's climax, set in downtown Los Angeles, involves Mose Jakande showing up with both a helicopter gunship and a drone. Somehow, a dangerous global terrorist like Jakande was able to enter U.S. airspace with two heavily armed aircraft and engage the heroes in a protracted battle across much of a major American city (and causing millions of dollars in property damage in the process), without drawing the attention of the U.S. military.
• Independence Day
  • An alien mothership nearly as big as the Moon isn't noticed by deep space radar until, in astronomical units, it is within spitting distance of Earth.
  • After the U.S. attack on the alien ship hovering over Los Angeles, a large number of alien fighters are able to make a surprise attack on the U.S. Marine airbase at El Toro even though the base should have been able to see them approaching with its radar.
  • In the sequel Independence Day: Resurgence it is Justified, as the Queen's mothership has a Cloaking Device, but there's no indication as to whether the original ship(s) also had them.
• Kingsman: The Golden Circle: Ten cruise missiles are fired from overseas at targets all over Great Britain, including two in London, in a Decapitation Strike against Kingsman. Never mind Her Majesty's Armed Forces, there isn't even any apparent reaction from the London police.
• Marvel Cinematic Universe:
  • Iron Man 3: The US Air Force is understandably concerned about unidentified craft entering American airspace, so the Mandarin's attack on Tony Stark's mansion with three helicopter gunships seems to be enabled by this trope. However, it's quite possibly Justified since the "Mandarin" is Aldrich Killian, who's conspiring with the Vice President, and the helicopters seem to be disguised as news choppers.
  • Captain Marvel takes place in the 1990s so nobody on Earth had the ability to actually respond to Ronon the Accuser attempting an Orbital Bombardment, but somebody besides Nick Fury should have at least remembered a squadron of Kree warships appearing and then retreating after one got blown up.
  • In both Avengers: Infinity War and Avengers: Endgame, Thanos' forces attack Earth with little acknowledgement outside of the core cast. This takes place only a few years after an Alien Invasion of New York saw the National Guard scrambled in response, yet the only army that reacts in either film is Wakanda's. If anything, you'd expect the rest of humanity to be better prepared for an alien attack after the Battle of New York.
  • Black Widow: General Dreykov has somehow kept the Red Room hidden from its enemies by housing it in a giant flying fortress. It would be nigh-impossible to keep something so big protected from radar and spy satellites without the sort of high-level government complicity that would make it redundant in the first place.
• Star Trek Into Darkness: Earth is the capital world of the United Federation of Planets, and yet the USS Enterprise and the USS Vengeance are able to have a full-blown Space Battle in orbit of the Moon without any apparent reaction from the rest of Starfleet.
• Star Wars:
  • Exaggerated in Attack of the Clones. Not only is Mace Windu able to infiltrate Geonosis with approximately a hundred Jedi and take the Separatist leaders completely off-guard despite them having a whole droid army stationed there (which would presumably merit some defences), but Yoda is able to follow shortly after with an entire invasion force of clone troopers, complete with air support, armor, and artillery.
  • Zigzagged in the opening of A New Hope. The Imperial Star Destroyer crew are able to detect C-3PO and R2-D2's escape pod as they escape from the Tantive IV down towards the surface of Tatooine, but then opt to let it go because "no lifeforms aboard" were detected. Apparently, the Star Destroyer's sensors cannot detect droids, in a setting where they are commonplace (even aboard Imperial vessels).
  • In The Empire Strikes Back, the Millennium Falcon does not detect Boba Fett's Slave One pursuing it to Bespin, despite said ship being in visual range. This is even more questionable considering the Falcon is traveling at sublight speed so the trip may have taken anywhere from days to months.
• Mostly justified in Top Gun: Maverick: the Navy strike force uses the terrain to evade enemy radar on approach to the target and while Maverick and Rooster are escaping the enemy base in a stolen F-14 (it isn't addressed in the film but Tomahawk missiles are also designed to do this), and the more powerful radar on the E-2D Hawkeye flying overwatch is able to pick up the enemy Su-57s despite their stealth capabilities. However, no explanation besides Rule of Drama is given for why the last Su-57 pilot didn't pick up Hangman's F/A-18E lining up on him, although it's possible the pilot was just fixated on Maverick's F-14 and didn't notice Hangman's radar echo.

Live-Action TV

• Agents of S.H.I.E.L.D.: During the last five episodes of Season One, the cast are still able to travel around in the 'Bus' and the Jump-Jet, including, in the former's case, touching down at an LA airport, despite the fact that HYDRA's schemes have been revealed, with the U.S. military and its allies hunting down any remnants of SHIELD. What's more bizarre is that this explicitly becomes a plot point in Season Two, with Team Coulson having to steal a Quinjet as they can't use the Bus or other non-cloaked aircraft without detection.
• Doctor Who:
  • In "Smith and Jones", the Judoon ships approached and parked on the Moon without being noticed for days, and even then only when they teleported a London hospital up to them.
  • A giant flying replica of the Titanic soars over Earth in "The Voyage of the Damned" without anyone on Earth seemingly noticing, including the paranoid amateur astronomer the Doctor talks to on the street.
  • In "The Sontaran Stratagem", the Sontaran Mothership had spent at least a few months orbiting Earth and is only detected by the paramilitary group UNIT after they put out a signal poisoning every car on Earth.
  • The military space station from "A Good Man Goes to War" is unable to detect two space-faring airplanes flying nearby. Due to their lack of radar or any other type of sensor, their entire communications array is taken out before they can contact their fleet.
• Firefly: Played with in "Objects in Space". Jubal Early manages to board Serenity and immobilize most of the crew unnoticed, but Wash did detect his ship coming: he just didn't realize it, because Early hid in a sensor blind spot so all Wash got was "a weird heat bounce off our wake" which he chalked up to a glitch.
• Zig-Zagged in Stargate SG-1. Smaller Goa'uld ships often have cloaking devices, but on several occasions alien capital ships appear over Earth and go completely unnoticed by anybody not related to the Stargate program. In some instances, however, they seem to go unnoticed at first but it turns out in a later episode that outsiders did notice: the Russians are clued into the program's existence when they recover wreckage of Thor's flagship Beliskner from the bottom of the Pacific following one of their submarines going missing in a related incident (it was captured by Replicators and then sunk by the US Navy), and in season 8 an aerospace billionaire whose company did some subcontracting for the F-302 Space Fighter turns up with satellite images of the Battle of Antarctica. An amateur astronomer also picks up the attempted Colony Drop in "Failsafe" (hitting the other side of the trope since the military hadn't noticed it) but the Air Force convinces him to keep quiet.

Video Games

• Halo: Combat Evolved: In the third mission of the game, the Master Chief and a squad of Marine allies are ferried via Pelican to within a few kilometres of the Covenant battlecruiser Truth and Reconciliation. Given the advanced tech level of the Covenant, systems on the warship should have been able to detect this easily.
• Rogue Squadron II: Rogue Leader: The mission to steal the shuttle Tydirium for the attack on the Second Death Star involves the player flying a Y-Wing to an Imperial surface base. You approach the base by flying through a canyon to hide from Imperial sensors (and knock out supplemental radar stations inside the canyon with the Y-Wing's ion cannon), but no explanation is given for how you got to the planet surface without being noticed to begin with.
• Star Fox: Assault: Invoked in the mission "War Comes Home" when the Aparoids unleash radar jammers to block the heroes' counterattack. Fox has to manually destroy each jammer with a sniper rifle, and the radar becomes more reliable with every one taken out.
• Star Wars: The Old Republic: In the Knights of the Fallen Empire expansion, the Player Character, despite being wanted for the murder of Emperor Valkorion, is able to repeatedly infiltrate the Eternal Empire's capital planet Zakuul by shuttle with little more reaction than unskippable random Skytrooper raids.
• Warframe: In certain missions, the Grineer can invoke this with their Regulators — should the player be detected, the Regulators can disrupt the player's radar until they either move out of its range or destroy the machine.

Western Animation

• Monsters vs. Aliens: The villain Gallaxhar's honking massive starship seemingly just appears over Earth without anyone noticing it coming. By contrast, the movie opens with a relatively small meteor being easily detected and its point of impact accurately pinpointed by one small remote station.
• Star Wars: The Clone Wars:
  • Season 2 Episode 16 ("Cat and Mouse") features an inversion: Anakin and Obi-Wan use a stealth ship, fitted with a Cloaking Device rendering it invisible to radar, to try to slip past the Separatist blockade on Christophsis... But once the Separatist commander Admiral Trench realises what the Jedi are up to, he's smart enough to track the stealth ship's magnetic signature instead and lock onto it with homing missiles.
  • In the season 4 episode "Shadow Warrior", General Grievous deploys a detachment of Separatist landing craft on Naboo seemingly unnoticed. You'd think the inhabitants might have put something in place to detect enemy ships after the last time this happened.
  • Furthermore, in the episode "Crisis On Naboo", Count Dooku parks a Separatist transport shuttle directly above Naboo’s Royal Palace, where Chancellor Palpatine is staying, mere hours after he was kidnapped. Although, this can probably be excused due to the strong implications that Palpatine set the whole thing up to test Dooku against Anakin.
• The Transformers: The Movie:
  • The Decepticons are able to board an Autobot shuttle going to Earth without being detected, catching all its occupants by surprise. A later comic adaptation justifies it by making the shuttle go through a field of asteroids, which provide good cover for the Decepticons.
  • Unicron, despite being an actual planet is able to sneak up on a defenseless planet at the beginning of the film as well as the Autobot bases on Cybertron's moons and then Cybertron itself and in every instance nobody notices him and no sensors detect him before he reaches nomming distance. Possibly justified due to it eventually being revealed that he's a Physical God rather than simply a giant robot, so maybe he can only be detected when he wishes to be.