The U-2 and SR-71 were fast, high-flying reconnaissance aircraft, but the slow, low-flying YO-3A Quiet Star handled reconnaissance in its own way:
Acoustically undetectable from the ground when flying around 1,200 feet, the YO-3A silently observed troop movement in Vietnam. Some pilots have also said that they went unnoticed by the enemy just 200 feet below them.
Nearly silent, this reconnaissance aircraft would patrol in the dead of night with absolutely no lights on. Using a downward facing night vision aerial periscope, the two man crew would fly above the enemy, taking notes of what they saw as well as call in support and direct artillery fire if needed.
What made this aircraft so quiet was mainly its slow turning propeller and heavily modified exhaust. The muffler ran the length of the aircraft which enabled sound to be incredibly dampened. Everything about this aircraft was designed to reduce noise. Instead of using gears, a belt system powered the propeller and the low rpm engine kept things quiet while eliminating vortices. The Quiet Star also had radar absorbing paint and it was said that once the pilot switched off their transponder, the tower couldn’t pick them up on radar.
The YO-3A’s were successful in their missions and thanks to being nearly completely silent, never took a round or were shot down during their time in Vietnam. In fact, they would have been used more if they weren’t deployed so late in America’s involvement of the war.
A single plane is being restored and maybe is already up and flying.