One of the surviving MiG-21's at Berlin-Gatow, wearing its original pre-1990 LSK/LV colour scheme, is MiG-21US Mongol-B 256 (c/n 02695156). The MiG-21US came between the U and UM-model. It looked like a UM, but still had the Tumansky R-11 engine of the earlier U.