Ordinary seaman

1. A seaman in the British Royal Navy in the 18th century who had between one and two years of experience at sea. Later, a formal rank in the Royal Navy for the lowest grade of seaman, now obsolete.
2. The second-lowest rank in the United States Navy from 1797 to 1917, between landsman and seaman. Renamed "seaman second class" in 1917.
3. The rating for entry-level personnel in the deck department of a ship in the United States Merchant Marine. An ordinary seaman (abbreviated "OS") is considered to be serving an apprenticeship to become an able seaman.