Development of the AC-130 Gunship II was delayed by numerous problems resulting in an interim solution being put forward.  The USAF still had a number of ageing C-119 transport aircraft in service, mostly with Air National Guard and Air Force Reserve units.  It was decided that this aircraft could be modified to a basic gunship configuration in short order and could fill the requirement until the AC-130 was available in some numbers.  Under project Combat Hornet a total of 52 AC-119s were withdrawn from service for modification to Gunship III standard by Fairchild-Hiller.  The basic model was the AC-119G, 26 of which were produced.  This was followed by a further 26 examples of the more sophisticated jet engine-augmented AC-119K.  The 71st SOS was activated at Lockbourne AFB, Ohio and was manned largely by Air Force Reserve crews.  The Squadron deployed to South Vietnam in December 1968 and established its headquarters at Nha Trang with detachments at Tan Son Nhut and Phan Rang.  On 1 June 1969, with most of the reservists replaced by regular personnel, the 71st was redesignated as the 17th SOS.  It was soon discovered that the AC-119G was grossly underpowered for the task it was being called upon to perform and could not even maintain altitude on a single engine.  Its poor performance and lack of sophisticated avionics and weapons meant that the AC-119G was largely confined to operations within South Vietnam where it performed sterling work in the protection of remote outposts and Special Forces units as well as supporting troops in contact with enemy forces, mostly at night.  The AC-119K was fitted with two J-85 jet engines, 20mm Vulcan cannons, and improved radar and night vision devices including a FLIR system.  The first AC-119K was delivered to the 18th SOS at Nha Trang on 3 November 1969.  The AC-119K squadron concentrated its efforts on night armed reconnaissance over the Ho Chi Minh Trail in Laos.  By the end of 1970 AC-119 detachments were operating from Phan Rang, Tan Son Nhut, Da Nang and Nakhon Phanom.

The AC-119G was known as Shadow after its radio call sign while the AC-119K was known as Stinger.  The aircraft of the 17th SOS were handed over to the VNAF’s 819th Squadron in September 1971 and the 18th SOS’s aircraft formed the 821st Squadron in December 1972.