The 42nd Infantry Division (42ID) ("Rainbow") is a division of the United States Army National Guard. It was nicknamed the Rainbow Division because, during rapid mobilization for service in WWI, it was formed from 27 National Guard units from across the US. The division was engaged in four major operations between July 1918 and the armistice in November 1918, and demobilized in 1919. Since World War I, the 42nd Infantry Division has served in World War II and the global war on terrorism (GWOT).
The division is currently headquartered at the Glenmore Road Armory in Troy, New York. The division headquarters is a unit of the New York Army National Guard. The division currently includes Army National Guard units from fourteen different states, including Connecticut, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Rhode Island, and Vermont. As of 2007, 67 percent of 42ID soldiers are located in New York and New Jersey.