The 17th Cavalry Regiment was organized under the provisions of the National Defense Act of 1916 at Fort Bliss, Texas on 30 June 1916 and constituted on 1 July 1916. Brigadier General John J. Pershing had taken his columns into Mexico only a short time before and the need of cavalry troops was pressing. Thirty-two officers and seven hundred and ninety-one veterans from the 1st, 3rd, 6th, 8th and 14th Cavalry Regiments were transferred as the nucleus of the new regiment. Many of these were recalled from the Mexican Punitive Expedition and since all were experienced troopers, little time was spent in whipping the organization into shape. The regimental commander, Colonel Willard A. Holbrook, assumed command on 9 July 1916, on which date the men from the 8th joined the 17th Cavalry Regiment. Colonel Holbrook held command until he was promoted to the rank of major general.