The successor in the skies over Vietnam to the AC-47 Spooky gunship was the AC-119 Shadow which often carried the nickname "Big Dumb Brother" which was derived from a little known USAF evaluation program called Project Little Brother for a light, heavily armed ground-attack aircraft suitable for counter-insurgency roles. The hope was the South Vietnamese Air Force (VNAF) would be able to field this smaller gunship as well.
Based at Eglin AFB, USAF evaluators gathered a Cessna 337 Skymaster, a Cessna 206, a Beechcraft S35, a Piper Cherokee Six, all of which were leased from their respective manufacturers and retained in their civilian schemes. Also, a Cessna 0-1 Bird Dog and a Cessna 0-2A Skymaster were pulled from USAF training units at Eglin. Joining the mix was the American Electric Pirhana, a single prototype high performance attack aircraft weighing only 2000 lbs.
The Little Brother candidate aircraft flew missions over Eglin's extensive ranges with minigun pods, napalm, free-fall bombs, rocket launchers and various gun installations. The favored platform in the program was the Cessna O-2 and the proposed O-2C would have higher powered engines, armor/self-sealing tanks, a side firing 7.62mm Minigun as well as the sensors and electronics for a pilot and gunner crew to fly and fight the gunship mission.
By the early 1970s Project Little Brother wound down to a close, but the sensors and avionics developed would form the basis of the more capable night attack sensors that would end up on the AC-119 and AC-130 aircraft during the War.
Source: Gunships- The Story of Spooky, Shadow, Stinger, and Spectre by Wayne Mutza. Specialty Press, 2009, p61-65.