I moved my comment's from the "WARTHOG" Thread.
Before there was an SF Branch we all had conventional Army MOS's with a "3" or "S".
I can only comment on the ARPAC side of the house. Various place's had a requirement for an
OPS/INTEL NCO. If they couldn't get that slot approved to the TO&E or TDA, with ARPAC approval they would pay the TDY for the 1st GP
to provide a man.
That's how I got sent to MAC-THAI in '66-'67. That was one of the most interesting trip's for me, I learned about all kind of stuff going on in SEA. Our boss was an AF LTC, he ask me one day why the CG and I had such long discussion's. He couldn't understand why a GO would want to talk to an EM. Rumor was CG had another job with a 3 letter outfit.
I learned about operations that were ongoing and probably didn't stop until '75.