Complex sentence: During the 1960s it flew MiG-17 aircraft, and by the 1970s as SR-71 flights became an issue of concern it acquired 36 MiG-25P Foxbat planes.
Split into simpler sentences: During the 1960s it flew MiG-17 aircraft. By the 1970s as SR-71 flights became an issue of concern, the base was assigned 36 MiG-25P Foxbat planes.