This twin-engined propeller cargo aircraft was notoriously sluggish. The plane actually originally had been developed as an glider with no engines at all.

The first order of business was to update the two planes to the C-123K configuration. This involved bolting a extra jet engine under each wing.

The Air Force then hired E-Systems to turn the airlifters into “self-contained night-attack” aircraft. The changes were significant.

Most noticeably, E-Systems extended the plane’s nose by some 50 inches. This new snout housed state-of-the-art radars and cameras.

In addition, contractors tucked a weapon system inside the cargo bay. The Hayes International Corporation built a special dispenser that dropped cluster bombs through 12 chutes in the bottom of the fuselage.

Special exhausts and a dark camo paint job helped the plane stay hidden when flying at night. The aircraft also got armor able to deflect .30-caliber bullets.

But these conversions took time and only added to the sense of urgency. “THIS IS NOT AN OPTIMIZED WEAPON SYSTEM,” states an early progress report we obtained through the Freedom of Information Act.

Work on the second plane took longer than expected, according to monthly project summaries. In February 1967, the Black Spot managers told their superiors that they could have the aircraft ready in two months—but only if they decided not to install the extra jets and most of the new equipment.

The Air Force leadership understandably declined this offer. Still, the flying branch was eager to see what the new design could do and expected to buy 20 more if the project was successful.

Plans also existed for a follow-on model based on the larger C-130. This Black Spot II project never came to fruition.

While the second aircraft was undergoing work, crews trained with the first aircraft at Eglin Air Force Base in Florida in mid-1967. The second pseudo-bomber eventually arrived at Eglin the following year.

At around same time, the flying branch renamed the places NC-123Ks—the letter N indicating dramatic modifications.

In the fall of 1968, the two Black Spot aircraft flew missions inside the boxed area outlined in black. They actively searched for a single North Korean boat inside the crosshatched area on Aug. 26. Air Force art

In August 1968, the two Black Spot aircraft departed Eglin for their first overseas deployment. But instead of Vietnam, the planes landed at Osan Air Base in South Korea.

The Air Force wanted to see if the former transports could help spot North Korean commandos trying to sneak south by boat. Despite the armistice, the two Koreas remained technically at war—as they do to this day.

The South Koreans also were formally in charge of any operations during this uneasy “peace.” The Pentagon would only take over if the Korean People’s Army tried to invade en masse.

So the NC-123Ks couldn’t carry any bomblets and had to report any possible contacts to the Republic of Korea’s Navy. With almost no time to get acquainted, the Black Spot crews had a hard time communicating with their Korean allies and separating enemy boats from civilian fishermen.

The Air Force concluded that the Black Spot aircraft were not well suited to patrolling the high seas. Almost three months after arriving at Osan, the two aircraft left for their intended mission in South Vietnam.

By November 1968, the aircraft were bombing enemy positions, according to the official history of the Black Spot Task Force. The crews used their radars and night vision optics to find sampans and other small boats hiding in the Mekong Delta region.

The next month, the planes began covertly to hit targets in neighboring Laos. The following year, the two Black Spot bombers moved to Thailand to be better positioned to strike these new target areas.

In Laos, the experimental aircraft attacked enemy supply convoys along the Ho Chi Minh Trail. The Black Spot detachment joined a host of other specialized units flying other unique planes in the Pentagon’s “war against the trucks.”

In the first half of 1969, Black Spot crews flew more than 100 missions from Thailand and blew up more than 200 enemy vehicles. By the end of the year, the aircraft had been renamed again as AC-123Ks. The “attack” nomenclature better described the planes and their mission.