In September 1940, the United States reintroduced conscription in response to the increasing likelihood of entry into World War II. Personnel voluntarily enlisting into the United States Army could choose to voluntarily enlist into the Regular Army, National Guard of the United States, or Organized Reserve.
The Army of the United States saw a major expansion following the 7 December 1941 attack on Pearl Harbor. On 13 December 1941, legislation provided that personnel inducted into the United States Army under the terms of the Selective Training and Service Act of 1940 were, both retroactively and from that date on, considered to be serving in the Army of the United States.
