The Army of the United States or Armies of the United States is the legal name of the "land forces of the United States" (United States Constitution, Article 2, Section 2, Clause 1 and United States Code, Title 10, Subtitle B, Chapter 301, Section 3001) and has been used in this context since at least 1841, as in the title: General Regulations for the Army of the United States. The Army, or Armies of the United States includes: the Regular Army, Army National Guard, and the Army Reserve, (as well as any volunteer or conscripted forces).
The Army of the United States (AUS) was also used as the official name for the conscription (U.S. term: draft) force of the United States Army that may be raised at the discretion of the United States Congress when the United States enters into a major armed conflict. The "Army of the United States," in this context, was used in World War II, the Korean War, and the Vietnam War.
The "Army of the United States" (AUS) was established in February 1941, in response to the increasing threat of the United States entering World War II. The Army of the United States saw a major expansion following the December 1941 attack on Pearl Harbor. It was considered the successor to the National Army, which had been founded to fight in World War I and was disbanded in 1920.
The first commissioned officers of the Army of the United States were appointed from the Regular Army. The standard practice that these officers held a "permanent rank" within the Regular Army as well as a higher "temporary rank" while serving in the Army of the United States. A typical situation might be a colonel in the AUS holding the permanent rank of captain in the Regular Army. Another term for the AUS was "Theater Rank," held by officers deployed to the European Theater or serving in the Pacific.
Promotions within the Army of the United States were sometimes very rapid, and some officers were promoted as many as four to five times in the space of just three to four years. Dwight D. Eisenhower, who served as General of the Army, rose from a colonel to five-star general in three years. However, rank in the AUS could be revoked just as easily, with senior commanders who were relieved reverting to their permanent Regular Army rank. This was known as "loss of theater rank," with some instances of generals returning to the United States in disgrace or at least under a cloud, as only colonels or majors.
The enlisted force of the Army of the United States was also partially made up of Regular Army career soldiers, but unlike their officer counterparts, they did not hold any separate AUS rank and were considered as Regular Army only. Personnel enlisting in the United States Army could also choose to enlist as Regular Army, which required a longer service obligation. The draft forces of the U.S. Army were all Army of the United States personnel and were annotated by the abbreviation "AUS" in front of their service numbers and in the Component block 5 on their discharge papers. Regular Army personnel were denoted by the abbreviations "RA."
In 1946, with postwar demobilization, the Army of the United States was suspended, along with the draft. Officers from that point reverted to Regular Army rank and all enlisted personnel either were discharged from the AUS or reenlisted in the Regular Army. The Army of the United States was reinstated during the Korean War, but it was mainly confined to the enlisted forces. Most commissioned officers in the Korean War held Regular Army rank only.
On its reinstatement for the Korean War, the Army of the United States consisted of conscripts in the Regular Army, with the National Guard and Army of the United States existing simultaneously in the same theater. The system of Service Numbers was as follows:ER: Enlisted Reserve
OR: Officer Reserve
NG: National Guard
RA: Regular Army
US: Army of the United States
For the Korean War, the Army of the United States changed its abbreviation to "US," replacing the older "AUS."
The last use of the Army of the United States was during the Vietnam War. It was disbanded in 1974, one year after US forces withdrew from the Republic of Vietnam.
The Army Reserve (USAR) and Army National Guard (ARNG) remained separate components during the modern era of conscription and their members continued to use their unique identifiers except in those cases in which officers were appointed or commissioned into a higher grade of rank while on active duty serving in a Regular Army unit. For example, during the war in Vietnam, a graduate of Army ROTC, commissioned as a USAR 2d lieutenant and serving his initial active duty tour, could be promoted to 1st lieutenant, or even captain, with a "temporary," active duty (i.e., AUS) commission while still holding the permanent, or USAR rank of 2d lieutenant. Another example would be an ARNG officer serving on active duty might accept a commission in the Regular Army (RA) and then might be promoted one or two grades in the AUS above their RA grade. This possibility could result in situations in which an Army National Guard captain could be called to active duty and accept a commission as a Regular Army major, then be promoted in the AUS, holding a "temporary," active duty commission at a higher rank and could retire after 20 or more years of active duty as a lieutenant colonel or colonel, while actually only having met the time-in-grade requirements (and passed the promotion board selection screening process) for the Regular Army, or "permanent" rank of major.