On May 3, 1968, the first of four Air Guard fighter squadrons began arriving in Vietnam with their F-100s. In addition, 85 percent of the 355th Tactical Fighter Squadron -- on paper a regular Air Force unit -- were Air Guardsmen. The Air Guard units were quickly integrated into Air Force combat operations and performed well.
http://www.ang.af.mil/History/Features/CallUps.asp
Thanks Genyous. I do appreciate the corrections.