United States Volunteers also known as U.S. Volunteers, U. S. Vol., or U.S.V. were military volunteers enlisted in the United States Army who were separate from the Regular Army.
Starting as early as 1861 these regiments were often referred to as the Volunteer Army of the United States but not officially named (codified into law) that until 1898.
During the nineteenth century this was the United States federal government's main means for raising large forces of citizen-soldiers needed in wartime to augment the small Regular Army and organized militia and National Guard. The U.S. Volunteers were the forerunner of the National Army in World War I and the Army of the United States in World War II, the Korean War, and the Vietnam War.
The U.S. Volunteers did not exist in times of peace. Unlike the militia, which, under the United States Constitution, each state recruited, trained, equipped, and maintained locally, with regimental officers appointed and promoted by state governors and not kept in federal service for more than nine months nor sent outside the country, the U.S. Volunteers were enlisted for terms of one to three years, and between 1794 and 1902 fought outside the country.
Regiments and batteries became known as "Volunteers" to distinguish between state and regular army units.
The great majority of soldiers who served during the War of 1812 were volunteers, or members of state militia who were federalized for portions of the war period. There were also volunteer units directly raised by the federal government.
U.S. Volunteers were seen as "temporary regulars" because they were not state troops but rather augmented the Regular Army.
GENERAL ORDERS No. 15., WAR DEPARTMENT, Adjutant General's Office, Washington, May 4, 1861.
The President of the United States having called for a Volunteer Force to aid in the enforcement of the laws and the suppression of insurrection, and to consist of thirty-nine regiments of infantry and one regiment of cavalry, making a minimum aggregate of (34,506) thirty-four thousand five hundred and six officers and enlisted men, and a maximum aggregate of (42,034) forty two thousand and thirty-four officers and enlisted men, the following plan of organization has been adopted, and is directed to be printed for general information:...
GENERAL ORDERS, No 126., WAR DEPARTMENT, Adjutant General's Office, Washington, September 20, 1862.
I..The following is the organization of Regiments and Companies of the Volunteer Army of the United States:
see Military leadership in the American Civil War#Militia and political leaders appointed to Union military leadership and American Civil War.
Each state was given a quota of "volunteer regiments" to be raised for service lasting from three months to three years, with quotas apportioned among the States according to population,
GENERAL ORDERS, No. 30. HEADQUARTERS OF THE ARMY, ADJUTANT GENERAL' S OFFICE, Washington, April 30, 1898.
I The following acts of Congress and Proclamation by the President are published for the information and government of all concerned:
An Act To provide for temporarily increasing the military establishment of the United States in time of war, and for other purposes.
Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That all able-bodied male citizens of the United States, and persons of foreign birth who shall have declared their intention to become citizens of the United States under and in pursuance of the laws thereof, between the ages of eighteen and forty-five years, are hereby declared to constitute the national forces, and, with such exceptions and under such conditions as may be prescribed by law, shall be liable to perform military duty in the service of the United States.
SEC. 2. That the organized and active land forces of the United States shall consist of the Army of the United States and of the militia of the several States when called into the service of the United States: Provided, That in time of war: the Army shall consist of two branches which shall be designated, respectively, as the Regular Army and the Volunteer Army of the United States.
The law provided for a presidential call for two-year volunteers, with quotas apportioned among the States according to population, and that militia units volunteering as a body had to be accepted as units into the Volunteer Army.