Editing Corps area (section)

===First Army Area===
First Army Area included First Army (Active) and Fourth Army (reserve on paper).

*'''[[First Corps Area]]''' replaced the Northeastern Department, and was headquartered in [[Boston Army Base]], Massachusetts, encompassing Maine, Massachusetts, New Hampshire, Rhode Island, Vermont and Connecticut. It was responsible for the mobilization, and administration of the [[First United States Army]] (1936–38); the Fourth Army, I Army Corps with 9th Division, 26th Division, 43d Division; XI Corps with three divisions; coast defense units of the First Coast Artillery District, some units of the GHQ Reserve, and the [[Zone of the Interior]] support units of the First Corps Area Service Command. First Corps Area was redesignated First CASC in May 1941.{{sfn|Clay|2010a|p=19}}
*'''Second Corps Area''' replaced the [[Eastern Department (United States Army)|Eastern Department]], headquartered at [[Fort Jay]] on [[Governors Island]] in New York City and encompassed New York, New Jersey, Delaware and from 1921 to 1937, the District of Puerto Rico. 
*Formations included the [[United States First Army]] (1921–36 and 1938–41); Fourth Army (1921–33); the [[II Corps (United States)]], with the [[1st Infantry Division (United States)|1st Infantry Division]], the only active division in the area; the [[27th Infantry Division (United States)|27th Infantry Division]] of the New York National Guard; and the [[44th Infantry Division (United States)|44th Infantry Division]] of the New Jersey, New York, and Delaware National Guards; and [[XII Corps (United States)]], assigned the [[77th Infantry Division (United States)|77th Division]], 78th Division, and 98th Division of the [[Organized Reserves]].{{sfn|Clay|2010a|p=26}} Also in the corps area was the [[21st Cavalry Division (United States)]] of the New York, Pennsylvania, Rhode Island, and New Jersey National Guards; the [[61st Cavalry Division (United States)|61st Cavalry Division]] of the Organized Reserves; the Second Coast Artillery District; and the Second Corps Area Service Command. 
*'''Third Corps Area''' variously headquartered at [[Fort McHenry]] and [[Fort Howard (Maryland)|Fort Howard]] in Baltimore, Maryland and included Pennsylvania, Maryland, District of Columbia and Virginia. Responsible for units of the First and Fourth Armies, III Army Corps ([[8th Infantry Division (United States)|8th]], 28, 29 Divisions) and [[XIII Corps (United States)|XIII Army Corps]] ([[79th Infantry Division (United States)|79th]], [[80th Division (United States)|80th]], [[99th Infantry Division (United States)|99th Division]]s, coast defense units of the Third Coast Artillery District, select units of the GHQ Reserve, and the Z.I. support units of the Third CASC.{{sfn|Clay|2010a|p=33}} From 15 October 1921, included the [[62nd Cavalry Division (United States)|62nd Cavalry Division]], Organized Reserves (also part of Fourth Army); included the [[2nd Combat Bombardment Wing|2d Observation Wing]], later 2d Wing, from 20 August 1920. From 1921 to 30 September 1927, [[Washington D.C.]] was withdrawn from the Third Corps Area and established as the District of Washington. After discontinuation, DC duties were taken on by the [[16th Infantry Brigade (United States)|16th Infantry Brigade]]. The [[14th Aero Squadron]] (or 14th Bombardment Squadron) was assigned to the Third Corps Area, August 28, 1933 and then transferred to the [[9th Bombardment Group]], on March 1, 1935. From 1940 to 1942, Third Corps Area was commanded by [[Walter S. Grant]],<ref>{{cite magazine |last=Birnie |first=Upton Jr. |date=October 1956 |title=Obituary, Walter S. Grant |url=https://digital-library.usma.edu/digital/collection/assembly/id/7659/rec/1 |magazine=Assembly |location=West Point, NY |publisher=Association of Graduates, United States Military Academy |pages=63–64 |via=West Point Digital Library |ref={{sfnRef|Birnie}}}}</ref> and the organization was designated the Third Corps Area Service Command in May 1941.