<P> At its greatest size the National Army had more than six million men . Promotions within the National Army were quick, with most United States Army officers receiving double and triple promotions within a space of only two years . Dwight D. Eisenhower entered the National Army as a captain and was a lieutenant colonel one year later . Douglas MacArthur also advanced quickly in the National Army, rising from major to brigadier general in two years . </P> <P> The Army entered World War I with very large divisions, often numbering more than 30,000 men (the 4th Division contained 32,000, for example) and consisting of two infantry brigades of two regiments each, with a total of sixteen infantry battalions per division . Each division also had three artillery regiments and an engineer regiment . </P> <P> The United States joined World War I in April 1917 on the side of the Triple Entente (British Empire, France, and Russia). Because of the necessary period of training before the units were moved overseas, the first elements of the American Expeditionary Forces arrived in June 1917 . Their first actions of the Western Front came in October 1917 . U.S. troops contributed to the offensive that finally broke through the German lines . With the armistice on 11 November 1918, the Army once again decreased its forces . </P> <P> The National Army was disbanded in 1920 and all personnel not subject to demobilization who had held ranks in the National Army were reverted to Regular Army status . George S. Patton, who had been a colonel in the National Army, returned to the Regular Army as a captain . Some, such as Douglas MacArthur, maintained their wartime rank in the Regular Army . For those keeping their wartime ranks the reality was, however, that they would usually remain at that specific rank for years . This often resulted in talented officers leaving service in the interwar years . </P>

When did the us begin sending large numbers of troops to join world war i in europe