The Cessna A-37 Dragonfly, or Super Tweet, is a jet-powered, light attack aircraft that was designed and produced by American aircraft manufacturer Cessna.
It was developed during the Vietnam War in response to military interest in new counter-insurgency (COIN) aircraft to replace aging types such as the Douglas A-1 Skyraider. A formal United States Air Force (USAF) evaluation of the T-37 Tweet basic trainer for the COIN mission was conducted in late 1962, after which the USAF concluded that it could be modified to effectively perform the role. The attack-oriented A-37 was directly derived from the T-37, roughly doubling in both all-up weight and engine thrust to permit considerable quantities of munitions to be carried, along with extended flight endurance and additional mission avionics. The prototype YAT-37D performed its maiden flight during October 1964.
While test results were positive, a production contract was not immediately forthcoming until an uptick in combat intensity and aircraft losses became apparent. An initial batch of 25 A-37As was deployed to Vietnam under the "Combat Dragon" evaluation program in August 1967, flying from Bien Hoa Air Base on various missions, including close air support, helicopter escort, forward air control (FAC), and night interdiction. The type proved itself to be effective in the theater, leading to the USAF issuing a contract to Cessna for an improved Super Tweet, designated the A-37B, in early 1967. It was largely operated over South Vietnam, as well as in neighboring Laos and Cambodia, typically flying close air support missions in coordination with US ground forces. The A-37 proved to be relatively low-maintenance and accurate and suffered relatively few combat losses.
Following the end of the conflict, the USAF's A-37Bs were transferred from the Tactical Air Command (TAC) to TAC-gained units in the Air National Guard and Air Force Reserve. The type was assigned to the FAC role and given the designation OA-37B. The type was eventually phased out in the 1980s and '90s, having been replaced in the FAC mission by the more formidable Fairchild Republic A-10 Thunderbolt II in American service. Various international operators, many of which were South American countries, also operated the A-37; it saw active use during the Salvadoran Civil War. Over 200 aircraft were also supplied to the Republic of Vietnam Air Force (RVNAF), and numerous A-37Bs were captured by North Vietnamese forces near the conflict's end.
Design and development During the early 1960s, American military involvement in Vietnam was growing, leading to strong interest from military officials in COIN aircraft.Darling 2005, p. 17. Existing platforms such as the Douglas A-1 Skyraider were less than fully satisfactory, in part because younger pilots, having been trained and used to flying jet aircraft, had difficulties adapting to the A-1's increasingly uncommon features for a frontline combat aircraft, such as a radial engine and a "taildragger" landing gear arrangement.Joiner 2009, p. 44. At the time, the Cessna T-37 Tweet was in widespread use by the military as a basic trainer aircraft.Joiner 2009, p. 43.Darling 2005, p. 9. In late 1962, the USAF's Special Air Warfare Center at Eglin Air Force Base's Hurlburt Field in Florida evaluated two T-37Cs for the mission.Darling 2005, p. 19.
The USAF determined the T-37 to be a promising COIN aircraft and expressed its interest in a prospective improved version that would be able to carry a much larger payload along with greater endurance and better short-field performance.Darling 2005, p. 20. These requirements meant the aircraft would have to be considerably heavier and thus necessitate the use of more powerful engines. To account for the drastic increase in airframe weight along with the need to a significant payload, as well, Cessna opted to double the aircraft's engine power by replacing its twin Continental J-69 engines with General Electric J85-J2/5 turbojet engines, each capable of generating up to of thrust. During 1963, the USAF awarded a contract to Cessna to produce two prototype aircraft, designated YAT-37D; these were essentially heavily modified T-37s.
Specific alterations made for the YAT-37D included the adoption of strengthened wings, the use of larger wingtip fuel tanks of capacity, additional avionics suitable for battlefield communications, navigation, and targeting, toughened landing gear that was suitable for rough-field operation, and the fitting of a General Electric-supplied GAU-2B/A "Minigun" Gatling-style machine gun capable of a rate of fire of 3,000 rounds/minute and 1,500 rounds of ammunition that was installed in the right side of the aircraft's nose behind a large access panel, along with an accompanying gunsight and gun camera. Perhaps most importantly, three stores pylons were installed on each wing that were compatible with a wide range of munitions.Darling 2005, pp. 20-21.
During October 1964, the first YAT-37D performed its maiden flight, followed one year later by the second prototype. The second prototype was equipped with four stores pylons under each wing as opposed to three, the first prototype was subsequently upgraded to this configuration, as well. Test results were good, but the USAF's interest in COIN aircraft had decreased over time. The program went into limbo for a time, with the second prototype "put out to pasture" at the National Museum of the United States Air Force at Wright-Patterson Air Force Base in Ohio.
The conflict in Southeast Asia continued to escalate during the mid-1960s. Losses of Douglas A-1 Skyraider close-support aircraft in the USAF, United States Navy, and RVNAF service proved to be greater than anticipated, which led to a revival in the USAF's interest in COIN aircraft. The YAT-37D seemed like a promising candidate for the role, yet the USAF felt that the only means of being certain was to evaluate the aircraft in real-world combat. At the time, this was a relatively unorthodox approach to military aircraft procurement. The USAF issued a contract to Cessna for a preproduction batch of 39 YAT-37Ds, opting for only a few minor changes relative to the prototypes, to be rebuilt from existing T-37Bs. These aircraft were initially designated AT-37D, but the designation was quickly changed to A-37A. The second prototype YAT-37D was pulled out of the USAF Museum and upgraded to A-37A standards as part of the test program.
The A-37A had a gross takeoff weight of , of which were ordnance. It was a relatively simple aircraft, avoiding any advanced weapon systems or the need for a complex training program to operate. The A-37A retained the dual controls of its T-37B ancestor, allowing it to be used as an operational trainer. In combat FAC operations, the second seat was occupied by an observer. Only a single crewman normally flew in the aircraft for close-support missions, which permitted a slight increase in ordnance.
Operational history
Vietnam War In August 1967, 25 A-37As were deployed to Vietnam under the "Combat Dragon" evaluation program, and flew from Bien Hoa Air Base on USAF "air commando" missions, including CAS, helicopter escort, FAC, and night interdiction. Combat loads included high-explosive bombs, cluster munition dispensers, unguided rocket packs, napalm tanks, and the SUU-11/A Minigun pod. For the majority of missions, the aircraft also carried two additional external fuel tanks on the inner stores pylons.
During this period, the A-37As flew thousands of sorties; none was lost to enemy fire, although two were wrecked in landing accidents. While the aircraft was formally named the "Dragonfly", many pilots called it the "Super Tweet". The Combat Dragon program was successful, but unsurprisingly, the combat evaluation revealed some of the deficiencies of the A-37A.Darling 2005, pp. 28-29. The most noticeable problem was that the aircraft lacked range and endurance. Other concerns were heavy control response during attack runs (the flight controls were not power-boosted) and the vulnerability of the aircraft's nonredundant flight-control system. Some pilots also criticised the machine gun as ineffective and negatively impacting the pilot's view.Joiner 2009, p. 46.Darling 2005, p. 32.
The USAF signed a contract with Cessna in early 1967 for an improved Super Tweet, designated the A-37B. The initial order was for 57 aircraft, but this was quickly increased to 127; the unit cost of these aircraft was roughly one-quarter of the McDonnell Douglas F-4 Phantom II all-weather fighter aircraft.Joiner 2009, p. 42. The A-37Bs were primarily intended to be supplied to the RVNAF as replacements for their A-1 Skyraiders. The A-37B prototype first flew in September 1967,Taylor 1968, p. 256 with deliveries to the South Vietnamese beginning in November 1968.Dorr and Bishop 1996, p. 153
The A-37Bs were all newly built airframes that were considerably stronger than those of the A-37A, capable of pulling six g instead of five, and were built to have a longer fatigue life of 4,000 hours. Field experience would demonstrate that 7,000 hours between overhauls could be tolerated. The A-37B weighed almost twice as much as the T-37C; a remarkable fraction of the loaded weight, , could be external stores. In practice, the A-37B usually operated with at least two and sometimes four underwing fuel tanks to improve combat endurance. The A-37B added a refueling probe to the nose, leading to pipes wrapped around the lower lip of the canopy, for probe-and-drogue aerial refueling. This was an unusual fit for USAF aircraft, which traditionally are configured for boom refueling. Other improvements included updated avionics, a redesigned instrument panel to make the aircraft easier to fly from either seat, an automatic engine inlet de-icing system, and revised landing gear. Like its predecessors, the A-37B was not pressurized.
To accommodate the increased weight, the A-37B was powered by General Electric J85-GE-17A engines, providing thrust each. These engines were canted slightly outward and downward to improve single-engine handling.Darling 2005, pp. 32-33. Air commando pilots in Vietnam operating the A-37A had found single-engine cruise an effective means of improving their flight endurance. Modifications were made to control surfaces to improve handling. To improve aircraft and crew survivability, the A-37B was fitted with redundant elevator control runs that were placed as far apart as possible. The ejection seats were armored, the cockpit was lined with nylon flak curtains, and foam-filled self-sealing fuel tanks were installed. To extend endurance, pilots were authorized to fly the A-37 on only one active engine, an uncommon practice outside of emergency situations at that time.Joiner 2009, p. 47.
The GPU-2/A and AMD cannon pods were tested with favorable results on the A-37B,"Seek Gun - AMD 420 30mm and GPU-2/A 20mm Gun Pod Test." dtic.mil. Retrieved: 14 November 2011. but reports indicate that such pods were either seldom or never used in operation.
The A-37 proved to excel at the close air support mission.Joiner 2009, p. 45. It was able to engage targets at speeds roughly 100 miles per hour slower than swept-wing fighters, which improved its bombing accuracy; pilots were reportedly able to achieve an average accuracy of . While the aircraft's slow speed was feared to make it more vulnerable to hostile ground fire, the A-37's relatively small size, atypical speeds, and relatively low altitudes combined to make it somewhat hard to hit effectively with gunfire. The A-37 required a relatively low level of maintenance compared to contemporary fighters—only two hours of maintenance for each hour of flight time, one-sixth as much as that of the McDonnell F-101 Voodoo, partially due to the convenient placement of multiple access panels at strategic locations.Joiner 2009, pp. 46-47.Darling 2005, p. 18.