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 it was concluded that it could be modified to effectively perform the role.

The attack-orientated 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.

While test results were positive, a production contract was not immediately forthcoming until an uptick in combat intensity and aircraft losses became apparent.

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 type were eventually phased out in the 1980s and 1990s, having been replaced in the FAC mission by the more formidable Fairchild Republic A-10 Thunderbolt II in American service.

[6] 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.

[7] Specific alterations made for the YAT-37D included the adoption of strengthened wings, the use of larger wingtip fuel tanks of 360 litres (95 US gal) capacity, additional avionics suitable for battlefield communications, navigation, and targeting, toughened landing gear that were suitable for rough-field operation, and the fitting of a General Electric-supplied GAU-2B/A 7.62 mm (0.300 in) "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.

[3] The USAF issued a contract to Cessna for a pre-production batch of 39 YAT-37Ds, opting for only a few minor changes relative to the prototypes, to be rebuilt from existing T-37Bs.

It was a relatively uncomplex aircraft, avoiding any advanced weapon systems or the need for a complex training program to operate.

[10] Combat loads included high-explosive bombs, cluster munition dispensers, unguided rocket packs, napalm tanks, and the SUU-11/A Minigun pod.

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.

In order to accommodate the increased weight, the A-37B was powered by General Electric J85-GE-17A engines, providing 2,850 lbf (12.7 kN) thrust each.

[15] Air commando pilots in Vietnam operating the A-37A had found single-engine cruise an effective means of improving their flight endurance.

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.

[17][18] The A-37 did not typically attract attention from the media, unlike many other USAF combat aircraft used in the theatre; one reason for this was that the type was never flown into North Vietnam, where hostile air defenses were proved to be challenging, claiming to have downed almost 200 F-4s and 300 F-105s by the conflict's end.

The type remained active in the theatre right up until the Fall of Saigon, shortly prior to which efforts were made to retrieve as many as possible before they fell into North Vietnamese hands.

Ninety-two of these were recovered by the US, while the other 95 aircraft would be operated by the Vietnam People's Air Force in missions over Cambodia and during the China conflict in 1979.

[32] On 20 April 2001, a Peruvian A-37B shot down a civilian Cessna A185E floatplane with a minigun under surveillance by CIA controllers who advised against engaging.

The Peruvian controller had the final authority in this situation, and he believed that the flight was carrying drugs out of the country, and so ordered the A-37 pilot to open fire.