The concept of firing sideways from a circling aircraft was not new — it had been shown to work in the 1920s and 1930s — but it was revived in earnest in the early 1960s. Bell engineer Ralph Flexman championed the idea, and after wind-tunnel and flight studies the U.S. Air Force ran live tests under Project Tailchaser. Captain Ronald Terry and a small team fitted podded 7.62mm miniguns to a C-47 and proved that a gentle left bank held the guns steadily on a ground target. Rushed to Vietnam for a combat evaluation in December 1964, the gunship’s results were so dramatic — broken sieges, shattered night attacks — that the type was adopted almost immediately and a dedicated squadron formed in 1965.

Each minigun was an electrically driven six-barrel Gatling firing the 7.62×51mm NATO round. A single gun could reach 6,000 rounds per minute; with three firing, Spooky could put thousands of rounds into a small area in seconds. Carrying on the order of 24,000 rounds, it is commonly said the aircraft could place a bullet into every square yard of a football-field-sized area in a few seconds — a vivid claim that is widely repeated and gives a fair sense of the density of fire, even if the exact geometry is hard to pin down. Every fifth round or so was a tracer, which is what produced the unbroken glowing line the troops below described.

Because the guns were fixed to fire out the left side, the aircraft itself was the aiming system. The pilot rolled into a steady left bank — a pylon turn — at roughly 3,000 feet and around 120 knots, pivoting the aircraft around an imaginary pole planted on the target. Sighting through a simple gunsight in his side window, he walked the fire onto the enemy while circling. It was deadly effective but left the slow, low, predictable gunship exposed to ground fire, which is exactly how several were lost.

Because the AC-47 was not built new but converted from surplus C-47 transports already in the inventory, there is no meaningful flyaway unit price for it — the “cost” was mostly the guns, ammunition-handling gear, flare systems and the labour to install them onto an airframe the Air Force already owned. No reliable public cost-per-flight-hour figure exists for the type either. Any precise dollar figure attached to an AC-47 should be read as an estimate; its real value lay in taking a cheap, abundant, decades-old airframe and turning it into a weapon that was, hour for hour, extraordinarily effective at night defence.