The Army of the United States
The Army of the United States (A.U.S.) is the land based military component of the Armed Forces. It was established by act of Congress during the earliest days of our country. In fact, the very first A.U.S. commander was General George Washington. Over the years, Congress and the War Department (present day DoD) redefined the A.U.S. and what groups were to be included in its membership. This occurred several times over the years, including in 1841 when Volunteer Corps  was added and in 1866 when U.S.VRC was included . Other notable changes included Militia being re-designated National Guard in 1903  and provision for the inclusion of draftees. It’s not well known but draftees were not members of the U.S. Army (U.S.A.) but of the A.U.S. until completion of their two years of mandatory service. Although the draft ended with the Vietnam War (1974), the A.U.S. continues in existence to support its other components. Today, the components of Army of the United States include:
1) The Regular Army. Subgroups: U.S. Army, U.S. Army Reserve, and the National Guard,
2) The Retired Reserve. Subgroups:
a. Persons retired from the Regular Army after the requisite time in service (20 years),
b. Persons who have served less than the requisite time in service but were placed on the retirement list due to age, and
3) Persons separating from service with a brevetted rank. For example, a person holding the rank of captain (O-3), but for meritorious service has been “brevetted” major (O-4), would enter into the Retired Reserve as a major but drawing the pay of captain. He/she would be entitled to use either the title Captain (USA) (Ret) or Major (AUS) (Ret).
5) The U.S. Volunteers. Only the President of the United States can call up the U.S. Volunteer units for federal active military duty and then only during times of war. Most notably, Civil War units largely fell into this category as well as Teddy Roosevelt’s “Rough Riders” during the Spanish American War, and finally,
6) The U.S. Veteran Reserve Corps (U.S. VRC).
A) By act of Congress in 1866, the U.S. VRC was included in the Army of the United States. That’s because thousands of disabled soldiers, brevetted soldiers, and U.S. Volunteers were placed on the retirement rolls. By congressional statute, members were appointed to the U.S. VRC by governors of states that had furnished troops to the Union war effort. Even though the U.S. VRC was largely melded into the regular army in 1869, the remnant remained to support retirees.
B) The present day U.S. Veteran Reserve Corps has claimed the mantle of its predecessor organization and received recognition from several governors and a U.S. senator as an historical representative of the Army of the United States.
 General Regulations for the Army of the United States, War Department, 1841
 Act of 39th Congress, Session I, Section 4-5, 1866
 The Militia Act of 1903 (32 Stat. 775), also known as the Efficiency in Militia Act of 1903 or the Dick Act