The Douglas AC-47 Spooky (also nicknamed "Puff, the Magic Dragon") was the first in a series of fixed-wing gunships developed by the United States Air Force during the Vietnam War. It was designed to provide more firepower than light and medium ground-attack aircraft in certain situations when ground forces called for close air support.

The AC-47 was a United States Air Force (USAF) C-47, (the military version of the DC-3) that had been modified by mounting three 7.62 mm General Electric miniguns to fire through two rear window openings and the side cargo door, all on the left (pilot's) side of the aircraft, to provide close air support for ground troops. Other armament configurations could also be found on similar C-47-based aircraft around the world. The guns were actuated by a control on the pilot's yoke whereby he could control the guns either individually or together, although gunners were also among the crew to assist with gun failures and similar issues. It could orbit the target for hours, providing suppressing fire over an elliptical area about 52 yd (47.5 m) in diameter, placing a round every 2.4 yd (2.2 m) during a three-second burst. The aircraft also carried flares it could drop to illuminate the battleground.

The AC-47 had no previous design to gauge how successful it would be, because it was the first of its kind. The USAF found itself in a precarious situation when requests for additional gunships began to come in because it simply lacked miniguns to fit additional aircraft after the first two conversions. The next four aircraft were equipped with ten .30 caliber AN/M2 machine guns. These weapons, using World War II and Korean War ammunition stocks, were quickly discovered to jam easily, produce large amounts of gases from firing, and, even in ten-gun groups, provide the density of fire of only a single minigun. All four of these aircraft were retrofitted to the standard armament configuration when additional miniguns arrived.

The AC-47 initially used SUU-11/A gun pods that were installed on locally fabricated mounts for the gunship application. Emerson Electric eventually developed the MXU-470/A to replace the gun pods, which were also used on later gunships.

In August 1964, years of fixed-wing gunship experimentation reached a new peak with Project Tailchaser under the direction of Captain John C. Simons. This test involved the conversion of a single Convair C-131B to be capable of firing a single GAU-2/A Minigun at a downward angle out of the left side of the aircraft. Even crude grease pencil crosshairs were quickly discovered to enable a pilot flying in a pylon turn to hit a stationary area target with relative accuracy and ease. The Armament Development and Test Center tested the craft at Eglin Air Force Base, Florida, but lack of funding soon suspended the tests. In 1964, Captain Ron W. Terry returned from temporary duty in South Vietnam as part of an Air Force Systems Command team reviewing all aspects of air operations in counter-insurgency warfare, where he had noted the usefulness of C-47s and C-123s orbiting as flare ships during night attacks on fortified hamlets. He received permission to conduct a live-fire test using the C-131 and revived the side-firing gunship program.

By October, Terry's team under Project Gunship provided a C-47D, which was converted to a similar standard as the Project Tailchaser aircraft and armed with three miniguns, which were initially mounted on locally fabricated mounts—essentially strapped gun pods intended for fixed-wing aircraft (SUU-11/A) onto a mount allowing them to be fired remotely out the port side. Terry and a testing team arrived at Bien Hoa Air Base, South Vietnam, on 2 December 1964, with equipment needed to modify two C-47s. The first test aircraft (43-48579, a C-47B-5-DK mail courier converted to C-47D standard by removal of its superchargers) was ready by 11 December, the second by 15 December, and both were allocated to the 1st Air Commando Squadron for combat testing. The newly dubbed "FC-47" often operated under the radio call sign "Puff". Its primary mission involved protecting villages, hamlets, and personnel from mass attacks by Vietcong (VC) guerrilla units.

Puff's first significant success occurred on the night of 23–24 December 1964. An FC-47 arrived over the Special Forces outpost at Tranh Yend in the Mekong Delta just 37 minutes after an air support request, fired 4,500 rounds of ammunition, and broke the VC attack. The FC-47 was then called to support a second outpost at Trung Hung, about 20 miles (32 km) away. The aircraft again blunted the VC attack and forced a retreat. Between 15 and 26 December, all the FC-47's 16 combat sorties were successful. On 8 February 1965, an FC-47 flying over the Bồng Sơn area demonstrated its capabilities in the process of blunting a VC offensive. For over four hours, it fired 20,500 rounds into a VC hilltop position, killing an estimated 300 VC troops.

The early gunship trials were so successful, the second aircraft was returned to the United States early in 1965 to provide crew training. In July 1965, Headquarters USAF ordered TAC to establish an AC-47 squadron. By November 1965, a total of five aircraft were operating with the 4th Air Commando Squadron, activated in August as the first operational unit, and by the end of 1965, a total of 26 had been converted. Training Detachment 8, 1st Air Commando Wing, was subsequently established at Forbes AFB, Kansas. In Operation Big Shoot, the 4th ACS in Vietnam grew to 20 AC-47s (16 aircraft plus four reserves for attrition).

The 4th ACS deployed to Tan Son Nhut Air Base, Vietnam, on 14 November 1965. Now using the call sign Spooky, each of its three 7.62 mm miniguns could selectively fire either 50 or 100 rounds per second.[1] Cruising in an overhead left-hand orbit at 120 knots air speed at an altitude of 3,000 feet (910 m), the gunship could put a bullet or glowing red tracer bullet (every fifth round) into every square yard of a football field-sized target in potentially less than 10 seconds.[2] As long as its 45-flare and 24,000-round basic load of ammunition held out, it could do this intermittently while loitering over the target for hours.

In May 1966, the squadron moved north to Nha Trang Air Base to join the newly activated 14th Air Commando Wing. The 3rd Air Commando Squadron was activated at Nha Trang on 5 April 1968 as a second AC-47 squadron, with both squadrons redesignated as Special Operations Squadrons on 1 August 1968. Flights of both squadrons were stationed at bases throughout South Vietnam, and one flight of the 4th SOS served at Udorn Royal Thai Air Force Base with the 432nd Tactical Reconnaissance Wing. The work of the two AC-47 squadrons, each with 16 AC-47s flown by aircrews younger than the aircraft they flew, was undoubtedly a key contributor to the award of the Presidential Unit Citation to the 14th Air Commando Wing in June 1968.

One of the most publicized battles of the Vietnam War was the Battle of Khe Sanh in early 1968. More than 24,000 tactical and 2,700 B-52 strikes dropped 110,000 tons of ordnance in attacks that averaged over 300 sorties per day. During the two and a half months of combat, fighters were in the air day and night. At night, AC-47 gunships kept up constant fire against enemy troops and provided illumination for the base.