Cota was commissioned as a second lieutenant in the Infantry Branch of the United States Army, and his first assignment was with the 22nd Infantry Regiment. Due to the outbreak of war Cota was quickly promoted to first lieutenant, then captain after only a few months. By the time he had accumulated 18 months of active duty, he was a major. He was assigned to become an instructor at the USMA shortly before the end of the war on November 11, 1918, serving there until 1920.