Corps area

For the century preceding 1920 the U.S. Army was geographically divided into series of Military Divisions, "Departments" and smaller "Districts" and Subdistricts. Departments and divisions were numbered or named for their geographic location. Before the War of 1812 these administrative units were geographically named starting with the Department of the East and Department of the West. About 1815, the areas were numbered until after the Civil War. After the Civil War, the system used until after World War I was again geographically identified; i.e. Department of the East or Department of the Missouri and subordinate units were called divisions or districts. The last reorganization of departments was done in 1917 after the beginning of World War I.

Authorized by the National Defense Act of 1920, which amended the National Defense Act of 1916, nine multi-state sized "corps areas" were established on 20 August 1920 by the U.S. Army Chief of Staff through War Department General Order Number 50. The corps areas were formed for administration, training, and tactical control of the army, replacing the six geographical (or territorial) military departments into which the continental United States had been divided since 1917 and with little variation since the Civil War. Three overseas commands: the Hawaiian Department, Panama Canal Department, and the Philippine Department continued to be identified as departments.[1]

The 1920 act was a realization that the mobilization of a citizen army could no longer meet the defense needs of the United States and for the first time placed an emphasis on peacetime preparedness. Yet with its passage, Congress never fully funded the program. But Congress did recognize the value of a professional officer education program by enhancing existing general service schools such as the Command and General Staff School at Fort Leavenworth, Kansas, and the Army War College at Carlisle Barracks, Pennsylvania. The act authorized the establishing new schools to meet modern military educational needs, such as the Army Industrial College in 1924. Thirty-one additional special service schools were established or improved to provide training to the various branches of the Army.

The act established the division as a basic Army unit, replacing the pre-World War I notion of the regiment in war planning. Tactically and administratively, each corps area commander was the senior army officer for his geographical area, typically functioning as a commanding general of an existing Regular Army corps or division in their area. During times of civil unrest, labor strikes, or natural disasters, corps area commanders provided Army resources needed to address the emergency.

Each corps area was allocated two "type" corps (with a standard table of organization) and six infantry divisions. The corps were numbered in accord with their corps area designation, i.e. I and XI Corps in the First Corps Area. The lower numbered corps (I through IX) consisted of one Regular Army and two National Guard divisions among the various states of the corps area. The higher numbered corps (XI through XIX) each consisted of three divisions, also assigned by state boundaries, of the newly established (but rarely funded) Organized Reserve. By 1925, in the face of steady Coolidge Administration and congressional budget cutting, the United States Army only had three active regular divisions nationwide; the remainder of its divisions, both regular and reserve components, only existed on paper.

The amended National Defense Act also grouped three corps areas into an "army level" mobilization organization whose boundaries were also identical for the two "type" armies located within them. For example, First, Second, and Third Corps Areas, and the First and Fourth (Field) Armies, comprised the First "Army Area". The 1921 mobilization planning that created the six field army headquarters did not envision a need for active field army-level commands in peacetime and thus the headquarters were constituted in the Organized Reserve rather than the Regular Army.

Until fully activated with its own headquarters staff, an army area was typically jointly staffed, headquartered, and commanded by the most senior corps commander in that area. Between 1927 and 1933 all six field army headquarters were deactivated as the Army wrestled with structure, mobilization, and manpower issues.

An army area included three corps areas, and in the early years was concurrently staffed and headquartered with one of the corps areas. For example, First Army Area headquarters staff was also the Second Corps Area headquarters staff based at Fort Jay at Governors Island in New York, New York.

Corps area commanding generals meet with the Chief of Staff and Secretary of War in Washington, D.C., 1 Dec. 1939.

General Douglas MacArthur, the Army's Chief of Staff, believed that the 1921 mobilization plan was based on unsound assumptions and that the Army required active field army headquarters before the start of any mobilization to manage the integration and training of subordinate units as they mobilized. He also concluded that the existing three army area/six army arrangement was too ponderous to field a force that might be needed in a hurry and that existing mobilization plans were not flexible enough to tailor to various war plans then in existence.

After a War Department study, MacArthur on 9 August 1932 constituted three new army headquarters in the Regular Army (the headquarters of the First United States Army was already constituted) and outlined the organization of what became known as the "four army" plan, which effectively abolished the three army area/six army system.

On 3 October 1940, the War Department transferred tactical command functions to General Headquarters, U.S. Army, separating the field armies from the corps areas. Corps areas were then limited to their Zone of the Interior functions as service commands and the field armies assumed control of all tactical units.

In 1942, after the start of World War II and by executive order, the army level organizations took to training or the field as home defense and combat commands under the control of Army Ground Forces. In March 1942, home defense and training activities were assigned to the newly formed Eastern, Central, Southern, and Western Defense Commands, which overlaid the existing Corps Areas. The geographical corps areas were redesigned as numbered service commands under the Services of Supply on 22 July 1942 (renamed in 1943 as Army Service Forces).[11] They served the Army's supply system, and performed administration, and "housekeeping" functions within the United States such as the issuance of Army serial numbers and the operation of induction centers and army posts located in the United States and its territories. By this time, the corps area boundaries and departments experienced some minor readjustments:

• Eastern Defense Command (co-headquartered with First Army until October 1943)
  • 1st Corps Area – ME, VT, NH, MA, CT, RI
  • 2nd Corps Area – NY, NJ, DE
  • 3rd Corps Area – PA, MD, VA, DC
  • 4th Corps Area – NC, SC, GA, FL, AL, MS, TN
• Central Defense Command (co-headquartered with Second Army)
  • 5th Corps Area – OH, IN, KY, WV
  • 6th Corps Area – IL, MI, WI
  • 7th Corps Area – MO, KS, NB, CO, IA, MN, ND, SD, WY
• Southern Defense Command (co-headquartered with Third Army until December 1943)
  • 8th Corps Area – AR, LA, TX, OK, NM
• Western Defense Command (co-headquartered with Fourth Army)
  • 9th Corps Area – WA, OR, CA, ID, MT, NV, UT, AK
• Hawaiian Department
• Panama Canal Department
• Philippine Department
• Puerto Rican Department

On 11 June 1946, Army Service Forces and the nine service commands areas it administered were abolished as the result of a long planned, post-war reorganization and downsizing. The service commands were replaced by six field army level organizations. These six Army Areas, though similar in name, operated on a functional rather than geographic basis but roughly followed along the old corps areas boundaries.

• First Army Area, headquartered at Fort Jay in New York, New York included ME, NH, VT, MA, RI, CT, NJ, NY and DE.
• Second Army Area, headquartered at Baltimore, Maryland included PA, MD, VA, WV, OH, IN and KY.
• Third Army Area, headquartered variously in rented office space in downtown Atlanta and in 1946 at Fort McPherson in Atlanta, Georgia included NC, SC, GA, FL, AL, TN and MS
• Fourth Army Area, headquartered at Fort Sam Houston in San Antonio, Texas included TX, AR, LA, OK, and NM.
• Fifth Army Area, headquartered at Fort Sheridan near Chicago, Illinois included IL, MI, WI, MN, IA, MO, KS, NE, ND, SD, WY and CO.
• Sixth Army Area, headquartered at Presidio of San Francisco, California included WA, OR, ID, MT, UT, NV and CA.[12]

The postwar Seventh United States Army in Germany and Eighth United States Army in Korea were outside the continental United States as they remain today, but under different names.

This organizational scheme served until the Army reorganization of 1973, with the creation of Forces Command and Training and Doctrine Command.

• Military organization
• Military History of the United States

• Clay, Steven E. (2010). US Army Order of Battle 1919–1941, Vol. 1: The Arms: Major Commands and Infantry Organizations (PDF). Fort Leavenworth, Kansas: Combat Studies Institute Press. This article incorporates text from this source, which is in the public domain.

• Conn, Stetson; Engelman, Rose C.; Fairchild, Byron (2000) [1964]. Guarding the United States and its Outposts. United States Army in World War II. Washington, D.C.: Center of Military History, United States Army.