Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. YJ-91 is the Chinese version of the Kh-31. YJ is short for Ying Ji meaning eagle strike. After purchasing 200 Kh-31Ps from Russia, China decided to develop its own version, because the original Kh-31 missile did not fully satisfy Chinese requirements. The resulting YJ-91 missile was developed by Hongdu Aviation Industry Corporation, the same manufacturer of the Silkworm missile. The experience gained from YJ-91 also helped the engine development of another supersonic missile indigenously developed in China, YJ-12, which is sometimes non-Chinese sources confuse it with YJ-91, as both share the same origin for their propulsion systems.