OS (Вахтенный матрос) / Third Officer (Третий помощник)

AB Seaman, OS

Officer in charge of a navigational watch on ships of 500 gross tonnage or more, Officer on watch (OOW), Second Officer, Third Officer

Officer in charge of a navigational watch on ships of 500 gross tonnage or more, Officer in charge of a navigational watch on ships of less than 500 gross tonnage, engaged on near-coastal voyages, OS

OS, AB Seaman