Definition
This variable indicates whether persons were engaged in active-duty military service in the armed forces of the United States during the World War I era (between April, 1917 and November, 1918). It does not include persons currently in the armed forces or those who performed military service in the National Guard, the Reserves (Army, Navy, or Marine), Reserve Officers' Training Corps, Citizens Military Training Camp, Merchant Marine, or other branch not a part of the regular military establishment, unless the individual was called up for active duty.