Following the acceptance of the N-156F as the fighter for the Military Assistance Program, trials with the first two N-156F prototypes had indicated the need for a stronger wing structure that could accommodate an additional stores station underneath each wing and a stronger undercarriage to accommodate the added load. It was expected that up to 6200 pounds of ordnance could be carried on four underwing pylons and one under- fuselage pylon.

These changes were built into the third N-156F (59-4989), which was given the designation YF-5A and became in effect the first production F-5A. At the same time, uprated J85-GE-13 turbojets were fitted, each offering 3050 lb.s.t. dry and 4080 lb.s.t. with afterburning. 59-4989 took off on its maiden flight on July 31, 1963 with Hank Chouteau at the controls. The first and second prototypes were subsequently brought up to F-5A production standards.

An initial production contract for 71 F-5s was awarded on October 22, 1962, and a further contract for 99 was awarded on August 27, 1963. About 1 out of 9 of these machines were to have been two-seat F-5Bs. Each plane was to have cost about $600,000, with the bill being paid partially or wholly by the US government under the provisions of MAP. A production rate of twelve F-5s per month was to be attained by the end of 1964, with first deliveries taking place early in 1965.

The first two genuine production F-5As (63-8367 and -8368) joined the test program at the end of 1963. Initial deliveries, beginning in April of 1964, were to the 4441st Combat Crew Training Squadron based at Williams AFB in Arizona, where the USAF trained the pilots and maintenance personnel of nations receiving F-5s. This base acted as the instructional centre for foreign personnel who were to act as instructors on the F-5 in their own countries.

The original configuration of the F-5A provided for only minimal fighter capability. In mid-1964, the Secretary of Defence directed a revision of the Specific Operational Requirement 199, requiring the addition of two internal 20-mm cannon in the nose and provision for nose fuel tanks and cameras. The two Colt-Browning M-39 cannon were fitted in the top decking of the nose, immediately ahead of the cockpit. This imposed a delay of four months while the cannon fit was designed and incorporated. The delay resulted in Category II and Category III testing taking place almost simultaneously between February and October of 1964.

The F-5A is optimized for the air-to-ground role and has only a very limited air-to-air capability. In the interest of achieving low cost, the F-5A was not equipped with a fire-control radar, the weapons being aimed by a simple optical sight acting in conjunction with a small Emerson radar ranging set installed in the extreme nose. The initial avionics fit was rather austere, the standard electronic equipment including an AN/ARC-34C UHF radio, PP-2024 SWIA Missile AVX, AN/AIC-18 interphone, J-4 compass, AN/APX-46 IFF and AN/ARN-65 Tacan receiver.

The first overseas order for F-5As was from Norway, which ordered 64 aircraft plus four attrition replacements on February 28, 1964. They differed in having a heated windshield, an airfield arrester hook, and provision for JATO.

The F-5A has very docile handling attributes. It is almost unspinnable, and exhibits little, if any, wing drop at the stall. By grouping the two J85 engines so closely together, Northrop has greatly reduced engine-out asymmetric effects.