What does DCOI mean? (Vietnam era)

as in 355 TAC FTR WG (DCOI) Inside parenthesis is exactly how it is engraved on silver plated mug/stein.

The full inscription reads:
SAWADEE
SGT CHRISTOPHER R. JOHNSON
355 TAC FTR WG (DCOI)
TAKHLI RTAFB THAILAND
1969 - 1970

I've deciphered everything except (DCOI).
355th Tactical Fighter Wing
Takhli Royal Thai Air Force Base


There is another engraved mug that reads:
USAF INTERCEPTOR WEAPONS SCHOOL
CHRISTOPHER R. JOHNSON
21 SEP 70 - 13 AUG 71

Any ideas why no rank in front of the name on the second mug, which is from a later date? Graduating Interceptor Weapons School means he became an instructor?
And from the inscriptions, I can't figure out what job he did. Was he a pilot? Ground crew? Radar? or...?

I hate it when things like this end up in a second-hand shop, especially when named. Had to 'rescue'. Also, haven't had any luck finding any info about him on-line.

 

He was not a pilot if a Sergeant.

"Deputy Chief of Operations for Intelligence (DCOI) office"

 

Yay! Thankyou!