J-XX (or J-X or XXJ) is a name applied by Western intelligence sources to describe a programme or programmes by the People's Republic of China to develop one or more new fourth- or fifth-generation fighter aircraft. In 2002, Jane's Defence Weekly reported that Shenyang Aircraft Corporation had been selected to head research and development of the new fighter, a claim repeated in New Scientist the same week. However, a 2006 article in Military Technology referred to three designs; two by Shenyang and one by Chengdu Aircraft Corporation.
According to the report from Jane's, development of the subsystems, including the engine and weapon suite for the next generation fighter, has been under way for some time. A photograph of a wind tunnel model published with the article showed a twin-engine aircraft with twin tails. The article text mentioned that the aircraft would carry its weapons internally like the F-22 Raptor, and New Scientist called attention to the angular, faceted features of the design, comparing them to the F-117 Nighthawk. Jane's also linked the programme with China's development of an engine with thrust vectoring capability.
The later report in Military Technology featured a picture of a completely different design, speculatively dubbed J-14 and said to be a Shenyang project, with the designations J-12 and J-13 being applied to (possibly competing) designs by Shenyang and Chengdu respectively.