From 1881 to 1891, Gaston served on frontier duty, which mainly involved military actions against the Apache and Sioux. He participated in the Spanish–American War, serving in Cuba from 1899 to 1902, and he later went to the Philippines. Gaston commanded permanent relief camps after the 1906 San Francisco earthquake. He graduated from the United States Army War College in 1912, and between November 1913 and April 1914, after traveling again to the Philippines between 1908 and 1910, he commanded the Cavalry School at Fort Riley. Gaston later commanded the 6th Cavalry Regiment and served at the border with Mexico and on the Pancho Villa Expedition in that capacity.