(covers information from several alternate timelines)
Operations officers are responsible for overseeing internal systems control, communications and sensors, while also coordinating the scheduling of resources, hardware, and system usage for an entire starship, outpost, or space station.(citation needed • edit) Operations officers manned the ops station.
The operations position was manned by a member of the command staff of a starship, regardless of seniority.(citation needed • edit) On the starship USS Enterprise-D, Lieutenant Commander Data served as the operations management officer and doubled as Second Officer, the most senior member of the ship's crew after the Captain and first officer. On the starship USS Voyager, Operations Officer Ensign Harry Kim was the most junior bridge officer.
As analytical operations relied upon knowledge of science and engineering disciplines, operations officers often performed the additional duties of a science officer, especially when a dedicated science officer was absent, as exemplified by both Data and Harry Kim. (TNG: "Conundrum"; VOY: "Caretaker", etc.) Operations officers also performed the duties of a communications officer. (citation needed • edit)