Home   Genealogy   Forums   Search   Contact
MHO Home
MHO Home
 17th Century
 18th Century
 19th Century
 American Civil War
 World War I
 World War II
 20th - 21st Century

 Write for MHO
 Search MHO
 Civil War Genealogy Database
 Privacy Policy

WWII Sections
MHO Home
 WWII Home

US Army in World War II Sections
 US Army in WWWII Home
  Introduction and Organization <<<
  Armor and Tank Types
  Cavalry and Infantry
  Artillery and AA Artillery
  Engineers and Logistics
  Manpower and Training

Rich Anderson Articles
US Army in WWII

Ads by Google

US Army in World War II
US Army in World War II
Introduction and Organization

by Rich Anderson


The US Army of World War II was created from a tiny antebellum army in the space of three years. On 30 June 1939 the Regular Army numbered 187,893 men, including 22,387 in the Army Air Corps. On the same date the National Guard totaled 199,491 men. The major combat units included nine infantry divisions, two cavalry divisions, a mechanized cavalry (armor) brigade in the Regular Army and eighteen infantry divisions in the National Guard. Modern equipment was for the most part nonexistent and training in the National Guard units varied from fair to poor.

The outbreak of war in Europe in September 1939 led to a gradual expansion of the Army. On 27 August 1940, Congress authorized the induction of the National Guard into Federal service. On 16 September 1940 the first peacetime draft in United States history was passed by Congress. However, the draftees were inducted for only one year. Fortunately, on 7 August 1941, by a margin of a single vote, Congress approved an indefinite extension of service for the Guard, draftees, and Reserve officers. Four months later to the day, Japan attacked Pearl Harbor.

On 7 December 1941 the Army consisted of 1,685,403 men (including 275,889 in the Air Corps) in 29 infantry, five armor, and two cavalry divisions. While this 435 percent increase was a magnificent achievement, shortages of equipment and trained personnel were still serious. Over the following three and a half years the Army expanded a further 492 percent, to 8,291,336 men in 89 divisions: sixty-six infantry, five airborne, sixteen armored, one cavalry, and one mountain infantry.
On 16 December 1944, forty-three divisions were deployed in the European Theater of Operations (ETO), including two airborne, ten armored and thirty-one infantry. Sixteen more divisions were preparing to join them. One armored division was on its way to the front. One airborne, one armored, and two infantry divisions were in England awaiting shipment to France. One airborne, three armored, and seven infantry divisions were in the final stages of training in the United States or were in route to Europe, but would not be deployed as complete units on the continent prior to the end of 1944.

At the end of the war in Europe there were a total of sixty-one divisions in the ETO: fifteen armored, forty-two infantry, and four airborne (one airborne division, the 13th, did not enter combat). Also, there were seven divisions in the Mediterranean Theater of Operations (MTO): one armored, five infantry (including one composed of African-American troops, the 93rd [designated Colored in the segregated Army, and a term that we will utilize without intent of prejudice in this essay]), and the 10th Mountain. There were twenty-one divisions in the Pacific Theater of Operations (PTO); one cavalry (dismounted), nineteen infantry (including one that did not enter combat, the 98th, and one that was Colored, the 93rd), and one airborne. 

Many of the problems associated with the performance of American units in World War II may be directly attributed to this. In general, the US Army was the best equipped and supplied in the war. However, the commonly accepted view that the US Army overwhelmed opponents by sheer numbers is not quite correct. US industrial expansion did provide a steady source of supply to the combat troops. However, logistical shortages, particularly in regards to tanks and artillery ammunition, and personnel replacements were a problem for American forces throughout the war.

Organization of the Army Ground Forces

The Army Ground Forces (AGF) was created in a major reorganization of the Army General Headquarters on 9 March 1942. AGF became responsible for the organization, training, and equipping of all Army units other than the Air Corps. The first commander of AGF was Major General (later lieutenant general) J. Lesley McNair (General McNair was accidentally killed by U.S. bombs while observing Operation COBRA on 25 July 1944). General McNair was the final arbiter on Army organization. He campaigned tirelessly to reduce overhead in U.S. divisions, insisting on as much streamlining as possible. There were two reasons for this. First, shipping space was at a premium for not only combat but also support units, and all supply items had to be shipped from the United States over great distances to foreign ports. Second, NcNair and other planners realized that the U.S. manpower pool was not inexhaustible. Industry and farming in the United States, and the massive expansion of the Navy, Marine Corps, Coast Guard, Army Air Corps, and Merchant Marine all absorbed vast numbers of men. The 213-division Army envisaged by the Victory Program of 25 September 1941 was never even close to being achieved; it proved to be difficult enough to man the 89 divisions eventually fielded.


An adjunct to General McNair's efforts to streamline the army was his effort to pool all non-divisional combat assets into homogeneous battalion-size units. Pooled units were to be held by corps or armies and were to be attached to divisions as needed. Field artillery, engineers, tanks, tank destroyers, antiaircraft artillery, and infantry units were all part of the pool. To facilitate pooling, in February 1943 all of the existing field artillery, antiaircraft artillery, and engineer combat regiments were broken up into separate battalions. The regimental headquarters were then utilized to form group headquarters. The group headquarters was intended to provide command and control for manageable aggregations of the large number of pool units.

A Note on Terminology

The convention utilized by the U.S. Army is that the designation of an army is spelt out (First), corps use Roman numerals (XX), divisions, brigades, regiments, battalions, and platoons all use Arabic numerals (90th), and companies, troops and batteries are lettered.

Corps, Army, and Army Groups

Twenty-four corps were activated by the end of the war, all except the XXXVI Corps served overseas. Three were originally formed as armored corps, of which the I Armored Corps was inactivated in Morocco and its personnel utilized in the formation of the Seventh Army, the II Armored Corps became the XVIII Airborne Corps, and the III Armored Corps became the XIX Corps. The other corps organized were the I-XVI, XX-XXIV, and XXXVI.

Twelve army headquarters eventually existed. By 1945, the First, Third, Seventh, Ninth, Fifteenth, and First (Allied) Airborne Armies were operational in the ETO, the Fifth was in the MTO, the Sixth, Eighth, and Tenth were in the PTO, and the Second and Fourth Armies were in the United States with training missions.

Finally, four army group headquarters were formed. The 6th and 12th Army Groups served in the ETO and the 15th Army Group in the MTO.

With few exceptions, all the armies and corps were organized by the AGF or existed in the Regular Army or Organized Reserves at the start of the war. However, the Fifth, Sixth, and Seventh Armies, First (Allied) Airborne Army, and all of the army groups were activated overseas.
* * *
< Previous Page

Next Page >

* * *

Copyright © 2000 Rich Anderson.

Written by Rich Anderson. If you have questions or comments on this article, please contact Rich Anderson at:

About the author:
Richard C. Anderson, Jr. works as the Chief Historian at the The Dupuy Institute (a non-profit organization dedicated to scholarly research and objective analysis of historical data related to armed conflict and the resolution of armed conflict. The Dupuy Institute provides independent, historically-based analyses of lessons learned from modern military campaigns.

Published online: 2000.
Last Modified: 02/11/2007.

* Views expressed by contributors are their own and do not necessarily represent those of MHO.
© 2018, LLC Contact Brian Williams at: