History

Formation of the “Rainbow” division was authorized on August 1, 1917, less than two months after creation of the AEF’s first operational division, the 1st US Infantry Division, “the Big Red One.” That unit had been formed by the amalgamation of regular army units. Secretary of War Baker asked that the new unit have the best trained men possible and that it represent all parts of the country. Major Douglas MacArthur, who worked for Secretary Baker, suggested amalgamating elements of the National Guard as had been done with regular army soldiers. Accomplished quickly, the War Department cherry picked Guard units that had received training on the Mexican Border. They came from 26 states and the District of Columbia. Assembly at Camp Mills, Long Island began on August 30, 1917 and was completed on September 13. Given the number 42, it was named the “Rainbow” Division when MacArthur described it as stretching like a rainbow across the United States.