FORT RUCKER, Ala. -- Before the advent of unmanned aircraft systems, pilots were the literal eyes and ears in the skies to provide valuable intelligence that would shift the course of many conflicts throughout the world.

One of the most successful tools for surveillance and observation was the Lockheed Missiles and Space Company YO-3A aircraft, which was a surveillance aircraft designed to fly silently over the skies of Vietnam, and was one of the first to employ state-of-the-art technologies that paved the way for modern-day surveillance, according to Bob Barlow, U.S. Army Aviation Museum volunteer and former Aviator.

"The (YO-3A) was a follow-on to the QT-2 program -- since it was so successful -- to build a more capable silent aircraft that would carry better sensors, have better range and provide better visibility for the crew," said Barlow.

The Army was the designated agency to develop the YO-3, with potential operators from all branches of service. The development was initiated in 1968 with the first test flight in December of that year.

Unlike the QT-2, the YO-3A sported more advanced features, including a front-mounted engine with a 210-horsepower rated Continental IO-300 reciprocating engine; a night vision aerial periscope with infrared illuminating spotlight; the first-ever airborne laser target illuminator in a production aircraft; and a gimbal-mounted, six-inch double viewing prism -- the largest ever made at the time -- that was capable of viewing a full 360 degrees, as well as 90 degrees up and 105 degrees down.

The first aircraft started out with a six-blade propeller system, but it was soon discovered that in the heat and humidity of Vietnam, the aircraft didn't have very good takeoff performance because the propeller system didn't have enough authority to "bite the air," said Barlow.

"So, they went to a three-bladed prop with a very broad blade, and that gave them better take-off performance," he said. "Before the three-bladed propeller, the aircraft had to roll almost a mile to get into the air and the three-bladed prop cut that distance about in half."

One thing the YO-3A did share with its predecessor was the long wingspan -- about 57 feet -- that allowed for better gliding performance when on reconnaissance, but that's where the similarities ceased, said Barlow. The YO-3A also featured internal antenna to reduce noise and drag, as well as a 26-foot exhaust, which extended down the starboard side of the fuselage.

"Each cylinder discharges directly into this exhaust, and it baffles the sound and attenuates it, so at the end the exhaust, the gas velocity is virtually zero -- that's how effective it was," said Barlow.

Although the aircrafts near-silent flight capabilities were impressive, even more impressive was its ability to see at night, said the museum volunteer.

"There were two systems that were developed for this aircraft -- the first was the night vision aerial periscope," he said. "That used a photo tube of very high sensitivity that could view light across a very broad spectrum, including infrared.

"That (system), which was mounted underneath the aircraft toward the front, was steerable in all directions and also incorporated an IR spotlight that could be turned on to look at whatever the sight was looking at," said Barlow. "Even with the IR turned off, the NVAP was so sensitive that it could detect a candle flame at a distance of over a mile, even on a moonlit night."

The viewing prism was also developed specifically for this aircraft and had such a wide viewing spectrum that, as pilots were approaching a target, the observer could keep an eye on a target during approach and as they flew away.

There were 11 YO-3A aircraft deployed to Vietnam in 1971, and with these new technologies, the YO-3A was so successful in its mission that the aircraft were able to fly a total of 1,116 missions and were never engaged by enemy fire, said Barlow.

"It was just that good at what it did and, as far as we know, the aircraft were never even detected," he said.

Although the aircraft was a success, the YO-3A wasn't developed any further for use after Vietnam. But that doesn't mean its development wasn't instrumental in shaping modern-day Aviation.

"If you look at the features of this aircraft -- the very efficient, long, high-aspect ratio wings, the sensor package it has, the propeller drive -- you can see all of this going into today's generation of UAS," said Barlow. "All of this was essential for the development of the UAS we know today.

"The technology and experience gained by these aircraft have been used in the development of future surveillance platforms -- the groundbreaking optics packages were ahead of their time," he said. "Sometimes when the technology arrives, the mission for what it was intended no longer exists, but all of that information goes into a databank and is rolled forward for use in other programs successfully. All of this is part of the Aviation Branch story."