By 1965 the Northrop F-5 Freedom Fighter light fighter-bomber had already been successfully exported, being used by or on order for over a dozen air forces.  However, some critics claimed that although the Department of Defense was eager to promote the aircraft for overseas sales, the USAF had not ordered any F-5s.  To answer these critics and further prove the capabilities of the aircraft, Secretary of Defense Robert McNamara ordered an operational evaluation of the F-5 in Southeast Asia under a project named Skoshi Tiger.  On 22 July 1965 the 4503rd TFS (Provisional) was formed at Williams AFB with 12 F-5Cs.  This variant was simply an F-5A with a few modifications, including an in-flight refuelling capability, the addition of armour plating and some changes in avionics and ordnance fits.  The Squadron left Williams on 22 October and arrived at Bien Hoa four days later, flying its first combat missions later the same day.  The combat evaluation was planned to last just over four months, after which the aircraft would then return home.

The evaluation included a deployment to Da Nang from 1 January 1966 for experience in forward operating base operations and missions over North Vietnam.  The Skoshi Tiger evaluation came to an end on 9 March 1966, the Squadron having flown 2,093 sorties from Bien Hoa and 571 from Da Nang in a total of 3,116 combat flying hours.  Only one aircraft was lost during the evaluation period and another 16 aircraft were damaged and 42 sorties aborted due to technical problems.  The evaluation was deemed a success and, as a recent increase in US strength had just been authorised, it was decided that the F-5 unit (renamed the 10th FCS in April 1966) would stay on in South Vietnam.  The F-5’s main disadvantage in combat in Vietnam was found to be its relatively short range and endurance.  However, its good load-carrying capability, survivability and cheapness eventually persuaded the US to supply the type to the VNAF in large numbers and the aircraft became the VNAF’s most potent weapon from 1967 onwards.