The Lockheed YO-3 Quiet Star is an American single-engined, propeller-driven aircraft that was developed for battlefield observation during the Vietnam War.

The YO-3A was designed to a United States Army specification of 1968, which called for an observation aircraft that would be acoustically undetectable from the ground when flying at an altitude of 1,500 feet (457 m) at night.

Lockheed Missiles and Space Company located in Sunnyvale, California was contracted to produce two prototype aircraft.

The exhaust gases are then moved through an acoustical fairing into a dissipating and resonating muffler continuing to the aft end of the fuselage.

[2] Nine of the eleven YO-3As produced operated in South Vietnam, at night, from 1970 to 1971 (Late June 1970 to September 1971) and, although three were destroyed in crashes, none were damaged by enemy fire or shot down.

Observations were initially made visually (80%), later followed on with a Night Vision Aerial Periscope developed by Xerox Electro-Optical of Pasadena, California.

Crew chiefs would monitor the YO-3A flying over the maintenance section prior to deployment, listening for rattles, whistles or other noises.

If any abnormal noises were heard, the aircraft returned to the runway, where duct tape and other measures were employed to quiet noticeable sounds.

The FBI eventually acquired the aircraft, and operated the type for several years, assisting the apprehension of kidnappers and extortionists.

NASA's Ames Research Center located at Moffett Federal Airfield in California acquired the YO-3A from the school in 1977.

In 2015, the aircraft was retired by NASA and sold by the General Services Administration at auction to the Vietnam Helicopters Museum.