As in the army, the ship's "centuria" was headed by a centurion with an "optio" as his deputy, while a "beneficiarius" supervised a small administrative staff. Among the crew were also a number of "principales" (junior officers) and "immunes" (specialists exempt from certain duties). Some of these positions, mostly administrative, were identical to those of the army auxiliaries, while some (mostly of Greek provenance) were peculiar to the fleet. An inscription from the island of Cos, dated to the First Mithridatic War, provides us with a list of a ship's officers, the "nautae": the "gubernator" ("kybernētēs" in Greek) was the helmsman or pilot, the "celeusta" ("keleustēs" in Greek) supervised the rowers, a "proreta" ("prōreus" in Greek) was the look-out stationed at the bow, a "pentacontarchos" was apparently a junior officer, and an "iatros" (Lat. "medicus"), the ship's doctor.