In addition to running the department, they were responsible for manning the Operations Station on the bridge and were a member of the senior staff.
Rank held for the position was normally dictated by the size and type of the vessel or station, but Lieutenant was the norm. Enlisted personnel would sometimes fill the role on small vessels.
Several divisions reported to Ops, including Communications.
They were closely with the Engineering Department as their duties often overlapped.
Operations Officers in the United Federation Marine Corps had a seperate set of duties.