It was kind of a catch-all command that they used when things got bigger faster. When I arrived in May 1966 we were attached to the 1st Cav. Went from there to MACV which was country wide. when that got too big it went to corps size control. For II Corps up in the highlands and coastal provinces Khan Hoa, Binh dinh, etc. It became IFFV , down south they had 2FFV. Maneuver battalions were 25 Div 101st 1st Cav. 4th Div replaced the 25th which went south. There were single units that were used in IFFV , 50th Inf a track unit was use a lot up by Bong Son area. My guess is that these guys are engineers, arty or something other than Infantry. We used to wear jungle fatigues with absolutely nothing on them, no patch, rank nothing, but infantry usually has the CIB on their blouse.