This was a tough one. Not sure if I have the answer, but here's what I found.
Check this page out, 2nd post from the top.
http://www.koreanwar.org/html/units/31fab.htm
Comments: Looking for anyone who served with HHB, 2d Bn 31st Arty when it was based at Ft Sill, Ok in the mid 1960's...This unit was then part of III Corps Artillery and its main mission was support to the Field Artillery School. We were assigned to 4th US Army and...we wore the red patch with the white 4 leaf clover on it.
Red Diamond w/ white 4-leaf clover = 4th US Army
https://www-perscom.army.mil/tagd/tioh/Army/04thArmy.htm
The base he was stationed at was most likely, Ft. Bliss, TX.
Looking up info about the Honest John missile, point more towards Ft. Bliss than Ft. Sill, OK.