freybearfreakfan, State Police uses a completely different set of unit letters. I think that list is for the local units in the Rockford area. For example Boy units for State are quartermaster/ fleet officers, Sam units are Safety Education units, and Victor units are the district Vin number officer.
I believe fairly recently the Accident Investigations units in each district had their radio IDs changed from their normal IDs to Ocean units. For example, in District 17, 17-43 became O-176 and 17-49 became O-177. They still do the normal patrol routines.
Maybe ISP had extra "O" units to hand out since they changed the radio techs to "T" units from "O" units (which using to be <District>R units)
Today here in District 5-Joliet I heard the female trooper say she is "Ocean-174, she used to be "574" on her license plate, she is really a cool person to listen to.....I must say these troopers work like dogs and the job is dangerous.....
ISP has formed regional crash reconstruction teams. Previously CRO's ( Crash Reconstruction Officers) were Troopers assigned to a particular district. The Trooper received additional training to become a certified CRO. The Trooper was assigned to regular patrol or admin duties but also assisted on serious auto crash scenes.
The Department has formed the Regional Reconstruction Teams which are not assigned to a particular district and are not on a district Roster. The teams are probably listed on the regional command roster or Springfield. The ISP probably assigned the O-Ocean designator in the same manner as is used to ID other specialist like TRT/SWAT, Crime Scene (F-Frank), P-Paul aircraft and M-Mary Motorcycle.
VASCAR2 is correct; O-173 is a regular trooper who also handles accident reconstructions. He is from Salem, but handles accidents throughout Region 7 of the Illinois State Police. You will hear him make a traffic stop, handle an accident investigation, or be on a sTEP Patrol.