North Vietnamese Mikoyan-Gurevich MiG-17 fighters (NATO reporting code "Fresco") at Phuc Yen Air Base, North Vietnam, circa in 1966.
USAF
<a rel="nofollow" class="external text" href="http://www.afhso.af.mil/">U.S. Air Force Historical Studies Office</a> publication <a rel="nofollow" class="external text" href="http://www.afhso.af.mil/shared/media/document/AFD-100526-034.pdf">Gradual Failure: The Air War over North Vietnam 1965-1966 (AFD-100526-034)</a> p. 223.