First Army (United States)

First Army is the oldest and longest-established field army of the United States Army. It served as a theater army, having seen service in both World War I and World War II, and supplied the US army with soldiers and equipment during the Korean War and the Vietnam War under some of the most famous and distinguished officers of the U.S. Army. It now serves as a mobilization, readiness and training command.

History

Establishment and World War I

The First Army was established on 10 August 1918 as a field army when sufficient American military manpower had arrived on the Western Front during the final months of World War I. The large number of troops assigned to the American Expeditionary Forces (AEF) required the activation of subordinate commands. To fill this need, First Army was the first of three field armies established under the AEF. The first commander was General John J. Pershing, who also served as Commander-in-Chief of the AEF. The headquarters planned and directed the first major American offensive, the St Mihiel Offensive (September 12 to 16, 1918). It later went on to fight in the largest and deadliest battle in the United States Army's history, the Meuse–Argonne offensive. Serving in its ranks throughout World War I were many figures who later played important roles in World War II. First Army, now under Lieutenant General Hunter Liggett, was inactivated on April 20, 1919, five months after the Armistice with Germany which ended hostilities.

Inter-war years

As part of the realization of the 1920 amendment to the National Defense Act of 1916, the Army Chief of Staff, General Douglas MacArthur, directed the establishment of six field armies that each commanded three corps areas that were geographically located. The "First Army Area" (First, Second, and Third Corps Areas) contained the First and Fourth Armies, the "Second Army Area" (Fourth, Fifth, and Sixth Corps Areas) contained the Second and Fifth Armies, and the "Third Army Area" (Seventh, Eighth, and Ninth Corps Areas) contained the Third and Sixth Armies. Between 1921 and 1932, the six field armies were constituted in the Organized Reserve rather than in the Regular Army, as the War Department did not see a need for active-duty field army headquarters in peacetime.