TR-3B is the designation attached in UFO lore to a supposed secret American aircraft: a large, nearly silent black triangle with lights at its corners, said to hover and to fly on antigravity or reverse-engineered alien propulsion. Enthusiasts often apply the name to any triangular formation of lights at night. In that use it serves as a terrestrial answer to black triangle reports, proposing that witnesses are seeing a classified U.S. craft rather than a visitor from elsewhere.

The "TR-3" label entered print in June 1991, when Aviation Week & Space Technology reported that a triangular reconnaissance aircraft designated TR-3A "Black Manta" might have supported F-117A operations in the Gulf War; Popular Mechanics followed that December. Space historian Dwayne Day later argued that no such aircraft entered service, that no photographs of it have been produced, and that the designation probably came from a misheard reference to the "Tier 3" reconnaissance drone effort. The "B" variant came later. In 1998 Edgar Fouché, who presented himself as a former Area 51 employee, described a TR-3B triangle built with reverse-engineered extraterrestrial technology, and he fictionalized his account in the novel Alien Rapture, co-written with Brad Steiger. French UFO cataloguer Patrick Gross has called the TR-3B "pure invention," arguing that its description followed what witnesses had already reported.

No government has acknowledged a TR-3B, and many of the triangle reports it is meant to explain have conventional explanations. Several pilots said the 1980s Hudson Valley lights were ultralight aircraft flying in formation; the 1997 Phoenix Lights were attributed to aircraft and military flares; the FAA linked 2000 reports in southern Illinois to an advertising blimp; and the British Ministry of Defence's Condign study attributed many sightings to atmospheric plasma. During the Belgian UFO wave of 1989 and 1990, F-16 pilots sent after a radar contact reported seeing nothing, and the wave's most famous photograph was later shown to be a hoax.

The TR-3B endures because real stealth aircraft such as the F-117 stayed hidden for years, which makes a still-secret triangle seem plausible to many observers. The name remained in steady use in 2026: researcher Richard Dolan revisited the subject, Reddit users labeled their own night-sky videos "TR3B," the independent short film series ANOMALY devoted its third episode to the craft, Space Force civilian employee Kyle Knopp discussed it on a podcast, and Steven Greer promoted a witness who said he had military contact with it. None of those accounts has produced a record confirming the aircraft exists.