Douglas AC-47 "Spooky"
Design and development

The AC-47 was a United States Air Force C-47 Skytrain (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. 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, where he could control the guns either individually or together, though gunners were also among the crew to assist with gun failures and similar issues. Its primary function was for close air support for ground troops, both U.S. and South Vietnamese. Once called into action, it could loiter, orbiting the designated target, sometimes for hours, providing suppressing fire. Coverage given by a Spooky was over an elliptical area approximately 52 yards in diameter, placing a projectile within every 2.4 yards during a 3 second burst.

Moreover, the plane carried 24,000 rounds of ammunition. Its high ammunition supply meant the AC-47 was highly unpopular with those on the receiving end of its fire, and extremely popular with the troops it supported (who nicknamed it Puff the Magic Dragon; there was even penned a version of the popular tune dedicated to the gunship). In addition to the miniguns, it also carried flares, which it could drop at will to light up the battleground.

Due to the age of its base airframe, the aircraft was very vulnerable to ground fire. Consequently, further gunship designs, the AC-119 gunship and the AC-130 gunship were developed, based around newer cargo airframes.

When the AC-47 was introduced, it was the first of its kind in and there were no preceding designs to gauge how successful the concept would be. When requests for additional gunships began to come in, the USAF found itself in a precarious situation. It simply did not have enough miniguns initially to fit additional aircraft after the first two conversions. The next four aircraft were in fact equipped with 10 AN/M2 .30 caliber (7.62 mm) machine guns. However, it was quickly found that these weapons, using ammunition stocks from WWII and Korea jammed easily, were extremely dirty in terms of gases produced from firing, and 10 guns could only provide the density of fire of a single minigun. When additional miniguns arrived, all four of these aircraft were retrofitted with to the standard armament configuration.

The mounting hardware initially used on the AC-47 simply used SUU-11/A gun pods that were installed on locally fabricated mounts for the gunship application. Eventually, Emerson Electric developed the MXU-470/A, a purpose built mount, which replaced the gun pods, and was also used on subsequent gunship aircraft.

Three MXU-470/A minigun modules fitted to an AC-47D. (Source: U.S. Air Force)