 He served in Mexico as part of the Mexican Punitive Expedition and saw action on March 19, 1916 at Guerrero; April 22, at Tomochic, Chihuahua, where he was awarded the Silver Star in an action against Villistas led by Candelario Cervantes; and at Piojo Canyon on June 20.In November 1916, Hickam left the 7th Cavalry to serve as a Professor of Military Science at the University of Maine and received promotion to captain of Cavalry, in May 1917, after the United States entered World War I.He joined the 18th Cavalry in July, but this unit was redesignated as field artillery.