China was receiving aircraft and technical help from the USSR. When Egypt and China seemed to be looking to the US for assistance, relations with the USSR ended. To keep aircraft development going in China, Egypt sent a Mig-21MF in return for a Romeo Class SSK sub. China reverse engineered the Mig-21MF and developed the J-7C/D. Externally the J-7D was almost identical but had some improved avionics and weapons controls, many J-7Ds were just upgraded J-7Cs. This J-7D originally was an operational night fighter under the Beijing MR (Military Region) at Huairen Air Field.
The Huairen Air Base is home to the PLAAF 15th Fighter Division that operates the Chengdu J-7 fighter. The former North China Military Region was renamed the Beijing Military Region and is one of seven military regions. With the Chengdu J-7 III main role being an interceptor these aircraft were assigned to protect the capital of Beijing should any enemy aircraft make it that far. Production of the Chengdu J-7 class ended in 2013 but is still flown by many countries including China.