MiG-17s were designed to intercept straight-and-level-flying enemy bombers, not for air-to-air combat (dogfighting) with other fighters. This subsonic (Mach .93) fighter was effective against slower (Mach .6-.8), heavily loaded U.S. fighter-bombers, as well as the mainstay American strategic bombers during the MiG-17's development cycle (such as the Boeing B-50 Superfortress or Convair B-36 Peacemaker, which were both still powered by piston engines). It was not however able to intercept the new generation of British jet bombers such as the Avro Vulcan and Handley Page Victor, which could both fly higher. The USAF's introduction of strategic bombers capable of supersonic dash speeds such as the Convair B-58 Hustler and General Dynamics FB-111 rendered the MiG-17 obsolete in front-line PVO service, and they were supplanted by supersonic interceptors such as the MiG-21 and MiG-23.