From The General and the Jaguar: Pershing’s Hunt for Pancho Villa: A True Story of Revolution and Revenge, by Eileen Welsome (Little, Brown, 2009), Kindle pp. 175-176:
The initial cavalry regiments tapped for service included the men of George Custer’s fabled Seventh, the Buffalo Soldiers of the Tenth, the horse soldiers of the Eleventh, and the troopers of the Thirteenth. Accompanying these mounted regiments would be the Sixth and Sixteenth infantries and two batteries of the Sixth Field Artillery. The heavy artillery hardly seemed worth the trouble: “To transport one gun required ten animals, which needed shoeing and forage, plus a dozen men to look after the mules as well as assemble and fire the gun,” points out military historian Herbert Molloy Mason. Supporting the combat troops would be a signal corps to establish communication, an ambulance company and field hospital for the wounded, engineers to build roads and bridges, and two wagon companies to haul supplies. (A wagon company consisted of 36 men, 27 wagons, 112 mules, and 6 horses.)
Army quartermasters from around the country worked frantically to locate supplies and ship them to Columbus. A boxcar of Missouri mules was requisitioned from Saint Louis. Twenty-seven new trucks were purchased from the White Motor Company in Cleveland and the T. B. Jeffreys Company of Kenosha, Wisconsin. Newly broken horses were entrained at Fort Bliss. Strange-looking vehicles that were actually the military’s first tanks were loaded onto railroad cars. Wagon parts, ordnance, radio sets, medical supplies, rations, and forage were also hunted down and shipped to Columbus.
Troops were sent from Fort Riley, Kansas; Fort Huachuca, Arizona; and Fort Oglethorpe, Georgia. At the request of President Wilson, Congress passed emergency legislation to increase the strength of the regular army from 100,000 to 120,000 men. Nearly all the additional men would be assigned to guard duty on the border or the expedition itself. Also dispatched to the border were Captain Benjamin Foulois and the country’s entire air force, which consisted of the First Aero Squadron and its eight Curtiss JN-3s, or Jennies. Flimsy as negligees and notoriously unreliable, the planes were dismantled and shipped by train. Captain Foulois posted ten riflemen at the front of the train and scattered more soldiers armed with rifles and pistols throughout the sleeping cars and the rest of the compartments.