In the mid 1960s, the North Vietnamese had shown the efficacy of the use of “guerilla interceptors” - small aircraft operating from camouflaged airfields to ambush enemy aircraft. While the PLAAF recognized the practicality of such operations and wished to apply them locally, the aircraft currently available for the role - MiG-17s, -19s, and -21s - were less than ideal. Thus, in 1969, Nanchang was issued requirements for a new lightweight fighter with a loaded weight under 4,500kg. Development proceeded and by August, they were performing wind tunnel testing, and by the next year, the design had started prototyping. The resulting J-12 was simple, coming in at 4,530kg. The J-12 was armed with a single 30mm and 23mm cannon in the wing roots, and was powered by a single WP-6Z turbojet. To simplify the design, it used only an optical gunsight, and lacked area ruling. To facilitate rough airfield operations, intake flow could be diverted through auxiliary ports on the fuselage sides.
When the J-12 first flew in December 1970, testing revealed a top speed of 1,300km/h, making the J-12 the lightest supersonic fighter ever to fly. Range was a short 688km, making the design effectively a point-defence interceptor. The only guided munitions that the aircraft could carry were simple IR-guided short range AAMs. In all, nine J-12s were built, with testing continuing until 1977. At this point, the shortcomings of the design were found to greatly outweigh its benefits, and the design was cancelled in favour of further development of the J-7 and J-8.