Lockheed YO-3A Quiet Star
Most people are familiar with stealth aircraft that are difficult to detect on radar due to their shape and general design. However, long before the F-117 stealth fighter took to the air, the US Army operated a completely different kind of stealth aircraft over the skies of Vietnam, one that relied on a lack of audible noise to remain undetected – the Lockheed YO-3A Quiet Star.
By the mid 1960’s the USA was becoming increasingly bogged down in the conflict in Vietnam. Despite their overwhelming firepower and complete superiority in every kind of weapons system, US forces were always having great difficulty in identifying the precise location of significant numbers of Vietcong to actually attack. The Vietcong were well aware that they simply could not complete in a conventional war against the might of the US forces, so they relied on hit and run tactics and then melted back into the thick, almost impenetrable jungle before heavy supporting weapons could be directed onto their location. A number of aircraft were used to try and identify the location of Vietcong formations, such as the O-1 Bird Dog, a military version of the Cessna 170, but these aircraft could easily be heard approaching Vietcong positions, giving them plenty of time to either disappear or get ready to direct weapons at the slow-flying aircraft. After a number of Cessna O-1 Bird Dogs were lost to ground fire, faster aircraft were used in this role, but this only tended to increase the level of audible warning and the greater speed made actually spotting the Vietcong even harder.
Lockheed Aircraft Corporation (LAC) were aware of these problems and following a directive from their senior management they decided the answer was to build an aircraft so quiet that its noise was drowned out by background sounds. Lockheed’s first proposal to build a quiet aircraft involved converting a single-seat Schweizer I-26 glider airframe by adding an air-cooled VW engine linked through a speed reduction system to the propeller. However this proposal, known as the Quiet Thruster 1 (QT-1), was rejected in favour of a two-seat aircraft with a conventional aircraft engine.
Lockheed’s second proposal was to convert a two-seat Schweizer 2-32 glider, powered by a four cylinder 100 HP O-200-A Continental engine and was known as the Quiet Thruster 2 (QT-2). This proposal was accepted and DARPA awarded a $100K contract to Lockheed for them to covertly build and test two aircraft within six months. The QT-2 was equipped with a muffler to help silence the engine, a four-blade 100ft diameter wooden propeller connected to the engine through a 3:1 speed reduction system. Initial flight tests near the US Navy riverine warfare training centre in the Sacramento River delta, where the engine noise from the QT-2 was only just audible, were declared a success – but there was only one place where a really realistic test could take place – Vietnam. In Jan 1968, under Operation Prize Crew, both QT-2s were shipped to Bien Hoa, a Special Forces air base northeast of Saigon, for the next phase of the operational testing which proved even more realistic than anyone could have imagined. On 31 Jan 68 the Vietcong launched the Tet offensive and during the intense fighting the QT-2 operated successfully at night without alerting the Vietcong.
Based on the experience of Operation Prize Crew, Lockheed reconfigured the design of the QT-2 for the final production aircraft. Using a low mounted wing, a large one-piece cockpit canopy, an engine in the nose and a retractable undercarriage, the resulting aircraft resembled a more conventional propeller aircraft and was given the official designation YO-3A. The pilot sat in the rear of the cockpit with the observer in the front where he could operate the payload – an early night vision system. Mounted in a turret underneath the fuselage was a stabilized image-intensifier with a wide-angle objective lens linked to a viewing scope in the observer’s position. The re-design of the production YO-3A resulted in an aircraft almost double the weight of the QT-2. To cope with the extra weight a more powerful 210hp air-cooled 6-cylinder Continental IO-360D engine was installed, linked to a constant-speed three bladed propeller, which gave the aircraft a top speed of 138mph, with a cruising speed of 110mph down to its quietest speed of 70mph.
However, although Operation Prize Crew was a clear success, by 1968 the continued US involvement in Vietnam had already begun to be seriously questioned by various politicians. Consequently, Lockheed were disappointed when in late 1968 the US Army announced a final production contract for only 14 aircraft. The YO-3As were quickly built and by the end of 1969 13 aircraft were shipped to Vietnam to equip the 73rd Surv Aircraft Company, 1st Aviation Brigade based at Long Binh, just northeast of Saigon. The remaining YO-3A was based at Fort Rucker, Alabama for advanced testing. Over the next couple of years the YO-3As flew around 1164 missions at night searching for the Vietcong – no planes were ever lost to enemy ground fire and, although shots were sometimes fired at the aircraft, no hits were ever recorded. The aircraft were withdrawn from Vietnam in Apr 1972 as part of the phased withdrawal and returned to the USA. A number were disposed of and today the best surviving example is in the Army Aviation Museum at Fort Rucker.
The YO-3A was a unique spyplane, designed for a specific role in a particular theatre of war. It was a genuine stealth aircraft before the term was actually later invented for the F-117 Nighthawk. The YO-3A aircraft had only a fairly brief operational life, but nevertheless proved that the concept and design actually worked in practice. I have considerable admiration for the YO-3A crews, flying a single-engined aircraft at night at a fairly low height over dense jungle teeming with Vietcong takes skill, raw courage and considerable nerve. The aircraft must certainly have startled many Vietcong as they squatted in the jungle having their evening rice bowl, and I would love to have seen the expression on their faces as suddenly, with no audible warning, a YO-3A swept silently across the night sky.