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 Viet Cong 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 Bong Son area of Vietnam's Central Highlands demonstrated its capabilities in the process of blunting a Viet Cong offensive. For over four hours, it fired 20,500 rounds into a Viet Cong hilltop position, killing an estimated 300 Viet Cong 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 (every fifth round) bullet into every square yard of a football field-sized target in potentially less than 10 seconds.
[2] And, 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.