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Background Information on U.S. Army Divisions in World War II
During World War II about 16,000,000 personnel served in the U.S. Military. Approximately 11,200,000 or 70% served in the U.S. Army (4,200,000 served in the Navy and 660,000 in the Marines.)
The U.S. Army
The U.S. Army was re-organized into three forces in March 1942:
- Army Ground Forces (AGF). According to the The Army Almanac, "Its mission was to provide ground force units properly organized, trained and equipped for combat operations." About 4,400,000 personnel were part of the Army Ground Forces during the war. They sustained about 80% of the U.S. Army casualties.
- Army Service Forces (ASF). The ASF, originally called Services of Supply, was responsible suppling and servicing the U.S. Army. Organizations under ASF included: corps of engineers, quartermaster corps, medical corps, signal corps, chemical warfare service, ordnance department, and the military police.
- Army Air Forces (AAF). The AAF was responible for the training and making ready the air component of the U.S. Army. The Army Air Forces became an independent service (U.S. Air Force) in 1947.
At it's peak in March 1945, the U.S. Army had 8,200,000 personnel. A comparison of Army Ground Forces strength with total U.S. Army strength is provided below.
| Date | Strength U.S. Army | Strength Army Ground Forces | Percent of U.S. Army |
| 31 Dec 1941 | 1,657,157 | 867,462 | 52.4% |
| 31 Dec 1942 | 5,398,888 | 1,937,917 | 35.9% |
| 31 Dec 1943 | 7,582,434 | 2,551,007 | 33.6% |
| 31 Mar 1945 | 8,157,386 | 2,753,517 | 33.8% |
The Army Ground Forces
Personnel in the Army Gound Forces were grouped into two areas: divisional forces and non-divisional forces. In March 1945, there was about 1,200,000 personnel assigned to divisions and 1,500,000 to non-divisional units.
The core combat arm of the Army Ground Forces was orginized around the division formation. The division was created to be the smallest Army organization capable of performing independent operations. Ninety-one divisions were formed by the U.S. Army in World War II. In general, a division contained about 15,000 troops. See below for a complete breakdown of a division.
Non-divisional forces included service units and some additional combat troops not initially assigned to a division.
Note: most service units were allocated across all U.S. Army organizations. For example, both the Army Service Forces and Army Ground Forces had engineer units. In addition, engineer units were part of divisions while other engineer units were part of non-divisional personnel.
Division
Combat troops of the U.S. Army are classified by the weapons and methods used in combat.
Divisional facts:
- There were 5 types of divisions: infantry, mountain, armored, airborne, and cavalry.
- 91 divisions were mobilized during the war: 68 infantry divisions, 1 mountain division, 16 armored divisions, 5 airborne divisions, and 2 cavalry divisions.
- All divisions were activated in the United States except for the following divisions: Philippine (activated in the Philippines), Hawaiian (activated in Hawaii and renamed the 24th division), 25th (activated in Hawaii from troops of the Hawaiian division), and Americal (activated in New Caledonia.)
- There were three major theaters of operation during the war: Pacific (22 divisions were deployed to the Pacific), Mediterranean (15 divisions), and Europe (61 divisions). Seven divisions served in both the Mediterranean and European Theaters (1st, 3rd, 9th, 36th, 45th infantry divisions; 82nd airborne; and 2nd armored.)
- Two divisions were disbanded or deactivated before the end of the war: the Philippine division was destroyed and disbanded on 10 April 1942; and the 2nd Cavalary division was activated and inactivated twice: 15 Apr 41 to 15 Jul 42 and 23 Feb 43 to 10 May 44.
- Three divisions did not enter combat: 98th Infantry division, 13th Airborne division, and the 2nd Cavalary division.
- By June 1946, 74 divisions were inactivated or disbanded leaving 17 divisions on active duty.
Division Components
All divisions of the U.S. Army originated from the following four sources:
Division Life Cycle
In general, a division went through the following phases during its existence:
- Cadre selection: A cadre of officers and men (about 1300 men or 10% of the division) were selected from a current division to serve as the nucleus of the new division.
- Division commander selection: The commanding general of the division was selected by General George Marshal, chief of staff of the United States Army.
- Cadre training: The cadre trained for a few months prior to activation.
- Officer fill out: Officer schools and replacement centers sent personnel to fill the complement of officers.
- Activation: The division was formally activated, that is, put in to existence so that it can be filled out.
- Division expansion: Draftees and enlistees were integrated into the division bringing it up to its authorized strength.
- Training: The division trained for a year.
17 weeks of basic and advanced training
13 weeks of unit training
14 weeks of combined arms training and large-scale exercises
8 weeks of final training - More training: The division participated in large scale, multi-division training exercises.
- Overseas movement: The division was moved to a port, loaded on transports and embarked to an overseas theater.
- Additional training: If possible the division trained for a few more weeks.
- Combat: The division moved to the front lines and entered combat.
- Relieved: Periodically the division was relieved from combat for rest, recuperation, re-equipping and retraining. After a break of a few days to a few months, the division re-entered the front lines.
- Inactivation or remained on duty: Personnel were returned to the United States and released from the Army and the division was de-mobilized. Most of the regular army divisions remained on duty in Europe or the Far East.
Casualties
The ten divisions with the most battle casualties are presented below. Casualties are defined as killed in action, wounded in action, captured and interned, and missing in action.
| Casualties | Division | Theater |
| 25,977 | 3rd Infantry Division | Mediterranean & European |
| 23,277 | 9th Infantry Division | Mediterranean & European |
| 22,660 | 4th Infantry Division | European |
| 20,993 | 45th Infantry Division | Mediterranean & European |
| 20,659 | 1st Infantry Division | Mediterranean & European |
| 20,620 | 29th Infantry Division | European |
| 19,466 | 36th Infantry Division | Mediterranean & European |
| 19,200 | 90th Infantry Division | European |
| 18,446 | 30th Infantry Division | European |
| 17,087 | 80th Infantry Division | European |
The five divisions with the most battle casualties in the Pacific Theater are provided below. Casualties are defined as killed in action, wounded in action, captured and interned, and missing in action.
| Casualties | Division | Theater |
| 9,212 | 7th Infantry Division | Pacific |
| 8,812 | 96th Infantry Division | Pacific |
| 7,461 | 77th Infantry Division | Pacific |
| 7,268 | 32nd Infantry Division | Pacific |
| 7,012 | 24th Infantry Division | Pacific |
Days of Combat
The ten divisions with the most days of combat are listed below.
| Days of Combat | Division | Theater |
| 654 | 32nd Infantry Division | Pacific |
| 600* | Americal Infantry Division | Pacific |
| 592 | 37th Infantry Division | Pacific |
| 531 | 3rd Infantry Division | Mediterranean & European |
| 521 | 1st Cavalry Division | Pacific |
| 511 | 45th Infantry Division | Mediterranean & European |
| 500 | 34th Infantry Division | Mediterranean |
| 443 | 1st Infantry Division | Mediterranean & European |
| 422 | 82d Airborne | Mediterranean & European |
| 400 | 36th Infantry Division | Mediterranean & European |
Sources: The Army Almanac: A Book of Facts Concerning the Army of the United States; Order of Battle, U.S. Army, World War II
