The MiG-23 was designed in 1964-66 as a successor to the MiG-21. In addition to a much more powerful engine, the MiG-23's most significant new feature was its variable sweep wing. Like the USAF's swing wing F-111, the sweep of the wings could be changed in flight. Fully spread, this gives a shorter takeoff/landing roll while carrying a heavier weapons load. With the wings fully swept back, the MiG-23 has greater speed. The wing has three sweep settings: 16, 45, and 72 degrees. The prototype first flew in April 1967 and MiG-23s began entering operational service in 1971.