bigpigeon.us webpage WWII US > Ground Forces > High-Level Organization, © 2023 by Robert A. Christiansen, updated by RAC 11 Jan 2023.
The high-level organizational structure of US WWII ground forces,
from army group to division, was as follows: Army Group > Army > Corps > Division
About army groups in WWII:
About armies in WWII:
  • The US First, Third, Seventh and Ninth Armies fought in the ETO.
  • The Fifteenth Army was a late, rear-area army in the ETO that saw little combat.
  • The Fifth Army fought in the MTO in Italy.
  • The Sixth and Eighth Armies fought in the Southwest Pacific Area in the War with Japan.
  • The Tenth Army, also containing Marine Corps units fought in Okinawa in the War with Japan.

About corps in WWII:
  • Napoleon Bonaparte invented the corps, an organization intermediate between an army and a division.
  • Because of the large number of divisions involved, many WWII maps show actions by corps but not by division.
  • The US and British identified corps by roman numerals.
  • https://apps.dtic.mil/sti/pdfs/ADA445769.pdf contains information about all WWII US corps commanders.

About divisions in WWII:
  • The Marine Corps fielded six infantry divisions, with an amphibious corps as the highest organizational level, and fought only in the War with Japan.
  • The United States fielded around 90 divisions in WWII; listing them throughout this document isn’t feasible.
The six kinds of US Army divisions :
  • Infantry - All infantry divisions had at their core three infantry regiments.
  • Light Armored - contained three armored infantry battalions, three tank battalions, and three armored artillery battalions. All light armored divisions served in the War with Germany.
  • Airborne Infantry - core consisted of two parachute infantry regiments and two glider infantry regiments.
  • Heavy Armored - only the 2nd and 3rd Armored Divisions, both of which served in the ETO.
  • Cavalry - only the 1st Cavalry Division, which served as infantry in the Southwest Pacific Area.
  • Mountain Infantry - only the 10th Mountain Division, which served in Italy.
I ignore the Heavy Armored, Cavalry, and Mountain divisions in the sequel.

Links to lists of army division-size and larger units:
Regarding WWII army infantry divisions:
  • The 1st - 9th, 12th, 24th, 25th, and 42nd  were Regular Army divisions.
  • The 23rd, 26th - 38th, 40th, 41st, and 43rd-45th were National Guard divisions.
  • The 63rd, 65th, 66th, 69th-71st, 75th-81st, 83rd-100th, 102nd-104th, and 106th were Reserve divisions. 
About specific infantry divisions:
  • The 12th Division, which included Philippine Scouts, Filipinos serving in the US Army, was earlier known as the Philippines Division and was lost in the Fall of the Philippines in 1942.
  • The 23rd Division was earlier known as the Americal Division and was organized in New Caledonia in 1942 from surplus National Guard units.
  • The 34th Division consisted of National Guard units from Iowa, Minnesota, Nebraska and the Dakotas. The regimental headquarters and 1 1/2 battalions of the 168th Infantry Regiment were captured in Tunisia in February 1943.
  • Two regiments of the 106th Division were captured early in the Battle of the Bulge.
  • The 92nd and 93rd Divisions were segregated; i.e. enlisted men were black and higher-ranking officers were white.