The Su-15TM (NATO code name: Flagon-F) Originally designed as an evolutionary development of the SU-9/Su-11 family with a more capable radar and twin engines, the Su-15 grew into a much larger and heavier aircraft . The Su-15TM was developed to supercede initial versions on the production line, with increased combat capability and featuring the Taifoon-M (RP-26) radar, ogival nose cone, and R-60 'dogfight' missiles. The upgraded SU-15TM permitted interceptions of targets flying at speeds of over 2500 klmh, and at altitudes over 75,000 feet. Deliveries of production SU-15TM's to PVO fighter units commenced from 1972. Gradually, togeather with the MIG-25P heavy interceptor, the Su-15 replaced the Su-9, Su-11, Yak-28P and Mig21PFM in the IA-PVO frontline inventory. Su-15's saw service with PVO units stationed in almost all borderside regions of the USSR, the high north and far east receiving priority, and remained one of the principle fighter types defending soviet airspace for many years. Electronics, engines, and armaments were continually upgraded so that the Su-15 remained a formidable high-speed interceptor, guarding Soviet airspace during the cold war in the 1970's and 80's. During the course of it's frontline career, the Su-15 participated in many successful interceptions resulting from border incursions, and occaisionally, used it's weapons systems in anger. About 700 su-15s remained in service by the mid-1980s, but these were gradually retired and replaced by the MiG-31 and Su-27 by about 1993.