China's military industrial capabilities have made significant advances unparalleled anywhere in the world since the 1990s, progress which came alongside the country's rapid economic rise. Chinese military aviation within a decade went from third world capabilities struggling to design a single reliable third generation fighter to building some of the world's most advanced combat aircraft within a decade. While the country's military industries have made great strides in all fields, from surveillance satellites to nuclear submarines, analysts drew attention one critical field in which China continued to lag behind others - jet engines. Early variants of China's J-11 and J-10 had to rely on Soviet Saturn AL-31 engines developed for the Su-27 and Su-30, and it took well over a decade for the country to develop with Russian assistance the Shenyang WS-10 to replace them.
China was well behind in the race to develop capable engines, and by 2010 when the WS-10 entered full service Russia had already developed the far more capable AL-41 for use on its Su-35. Indeed, China's subsequent purchase of a small unit of just 24 Su-35 fighters drew much speculation that the country needed the fighters to reverse engineer their AL-41 and develop equally capable platforms for its new fighters. With China also set to induct two fifth generation fighters in the 2010s, the J-20 and J-31, the country needed not only to acquire the technologies of Russian '4++' generation engines from the Su-35 - but also to develop fifth generation engines. Russia had developed an enhanced variant of the AL-41, the AL-41F1, for prototypes and early models its own fifth generation fighter the Su-57. The country was also developing the izdeliye 30, a more capable engine, to be installed on later variants of the fifth generation fighter after 2020. The United States too had in 2005 inducted the Pratt & Whitney F119 for its F-22 Raptor - allowing the heavy platform to supercruise (travel supersonically with a full payload and without afterburners).
It appeared that China could produce everything needed for its fifth generation fighters other than their engines, and the country's 'Made in China 2025' initiative called for massive investment in Aerospace industries - both civilian and military. The country sought engines which outperformed the F119 installed on the F-22 Raptor - which would make them the most capable in the world until Russia inducted its Izdeliye 30.
China inducted its first fifth generation platform, the J-20 air superiority fighter, in March 2017. While the fighter's induction was an impressive, making China one of only two countries in the world to produce stealth fighters, it was notable that its engines were advanced variants of the WS-10, the WS-10G, which in turn were based on Soviet AL-31 engines developed in the 1980s. While far superior to the original, enhanced with Russian assistance, the early J-20 engines still left much to be desired - particularly when compared to the F119.
In January 2018, after extensive efforts to develop a next generation engine, China was revealed to have finally built an engine worthy of the J-20. The engine notably included advanced stealth features such as serrated afterburner nozzles and interior flaps to minimize its radar signature - much like the F119. The WS-15 was designed to allow the J-20 to supercruise in the same way as the American F-22 Raptor, and was reportedly more capable in many fields that the F-119. Having mastered advanced technologies such as single crystal superalloy turbine blades and powder metallurgy superalloy turbine disks, the new engines are set to make the J-20 faster and more manoeuvrable - removing the most significant hurdle which prevents it from being developed into a platform superior to the Raptor.