The 15th Cavalry Division was created in February 1917 at Fort Sam Houston, Texas. It numbered in succession of the 1st–14th Divisions, which were not all active at its creation. Originally trained for deployment to Europe, its units were later converted into field artillery units. The division was deactivated on 12 May 1918. Its personnel and other assets were later used to form 1st & 2nd Cavalry Divisions. On 20 August 1921, as a result of lessons learned from World War I, the Army's Adjutant General, Major General Peter C. Harris, constituted the 1st and 2nd Cavalry Divisions to meet future mobilization requirements. However, the 2nd Cavalry Division was not subsequently activated, and remained in 'on-paper' organizational limbo for twenty years.