25 April 1962 – In 1962, the Kennedy Administration revived the requirement for a low-cost export fighter. The design effort was led by Northrop vice president of engineering and aircraft designer Edgar Schmued who previously at North American Aviation had been the chief designer of the successful North American P-51 Mustang and F-86 Sabre fighters. On 23 April 1962, the N-156F was determined the winner of the F-X competition (subsequently becoming the “F-5A”), which was selected on 24 April 1962 by the DOD for their military assistance program. The F-5A was ordered into production in October that year. 
Preliminary combat evaluation of the F-5A began at the Air Proving Ground Center, Eglin AFB, Florida, in mid-1965 under the code name Project Sparrow Hawk. One airframe was lost in the course of the project, through pilot error, on 24 June.
In October 1965, the USAF began a five-month combat evaluation of the F-5A titled Skoshi Tiger. A total of 12 aircraft were delivered for trials to the 4503rd Tactical Fighter Squadron, and after modification with probe and drogue aerial refueling equipment, armor and improved instruments, were redesignated F-5C. Over the next six months, they performed combat duty in Vietnam, flying more than 2,600 sorties, both from the 3rd Tactical Fighter Wing at Bien Hoa over South Vietnam and from Da Nang Air Base where operations were flown over Laos. Nine aircraft were lost in Vietnam, seven to enemy ground fire and two to operational causes.
Operations with 3rd TFW were declared a success, with the F-5 generally rated as being as capable a ground-attacker as the F-100, albeit having a shorter range. However, the program was more a political gesture that was intended to aid the export of F-5s, than a serious consideration of the type for US service. The Philippine Air Force had been watching the performance of the Skoshi Tiger and acquired 23 F-5A and B models in 1965. These aircraft, along with remanufactured Vought F-8 Crusaders, eventually replaced the Philippine Air Force’s F-86 Sabre in the air defense and ground attack roles.
Source: Wikipedia