A foreign national serving in a capacity required for normal operations and service on board a vessel or aircraft. Crewmen are admitted for twenty-nine days, with no extensions. Two categories of crewmen are defined in the INA: D1, departing from the United States with the vessel or aircraft on which he arrived or some other vessel or aircraft; and D2, departing from Guam with the vessel on which he arrived.

Crewman is a generic term for a crew member of an aircraft, naval vessel, military unit, or team of professionals attempting to accomplish a goal. In some science fiction, series (most notably Star Trek), Crewman is the lowest military rank onboard a spacecraft.