Not all folks that were drafted or enlisted were deployed to Viet Nam. Even some that requested duty there were denied. Others volunteered to do multiple tours there.
My husband attended Avionics school at Keesler AFB 1967-68 and fully expected to go straight to Vietnam upon graduation because he was one of the senior students.
When we got notification of the command assignment a week or so before the APO number, it was PACAF (Pacific Air Command), which included all of Southeast Asia.
Then when the base assignments came out, my husband called me from school with only the APO number. I went over to Family Services (where I volunteered) to look at the APO chart, and it was Hickam AFB Hawaii.
By the time he finished that 3 year assignment, Vietnam was winding down and he was sent to Florida instead.