1990's -- The A-10 Thunderbolt II is the first Air Force aircraft specially designed for close air support of ground forces. They are simple, effective and survivable twin-engine jet aircraft that can be used against all ground targets, including tanks and other armored vehicles. (U.S. Air Force photo by Senior Airman Greg L. Davis)
After a broad review of its tactical force structure, the U.S. Air Force decided to adopt a low-cost aircraft to supplement the F-4 and F-111. It first focused on the Northrop F-5 , which had air-to-air capability.  A 1965 cost-effectiveness study shifted the focus from the F-5 to the less expensive LTV A-7D , and a contract was awarded. However, this aircraft doubled in cost with demands for an upgraded engine and new avionics.