(US Army)

When you think of stealth aircraft, you probably think of something that's invisible to radar. Yes, that is a huge component of being difficult to detect in the skies today, but there's another element that comes into play when it comes to spotting a plane: noise.


Yeah, we know that sounds obvious, but hear us out. Think about any air show you've ever attended. You've heard just how much noise those planes put out — you'll often hear them well before you see them. There was one plane, however, that you'd have a hard time hearing — one that saw action over Vietnam. That plane was the YO-3A "Quiet Star" observation plane.

A total of 11 Quiet Stars were built — and all saw action over Vietnam.

(US Army)

Lockheed's unique plane was designed in every possible way to be a silent hunter. This plane didn't pack any weapons. Instead, it carried something even deadlier to enemy troops on the ground: a radio that enabled the two-man crew to call in artillery fire or air strikes.

So, how did they keep this aerial creeper so quiet? The plane was made mostly of fiberglass and used a show-turning propeller. The propeller was turned by using a belt-and-pulley system, eliminating the noise of more conventional systems. The observer sat in front with the pilot in the rear, an arrangement similar to that used on helicopter gunships, like the AH-64 Apache.

NASA used the YO-3A Quiet Star to measure the sound from other aircraft,

(NASA)

The Army took the Quiet Star to Vietnam in 1970. It operated low, often below 1,000 feet — well within the range of small arms, like the AK-47, that the North Vietnamese had in quantity. Surprisingly, this plane wasn't even shot at by the enemy — none of these planes took damage during the conflict. A grand total of 11 planes were built and sent to Vietnam, where they served through 1971.

The planes were then returned to the United States and some were acquired by the Louisiana Department of Fish and Game. While with that agency, these planes helped bring a number of poachers to justice. The FBI also used the YO-3A for surveillance on some high-profile cases, like locating Patty Hearst. NASA also used the Quiet Star to help measure the sound from other planes.

The NASA Quiet Star retired and was sent to a museum in 2015. Learn more about this silent hunter in the video below!