Regiment the following month. World War I came to an end soon afterwards, on November 11, 1918. Unable to fight overseas during the war, Collins commanded the 3rd Battalion, 18th Infantry Regiment in France in June 1919, and was assistant chief of staff, as a G-3 staff officer with the American Forces in Germany from 1920–1921. During this time, Collins served in the Army of Occupation in Germany. Between the wars Collins married Gladys Easterbrook in 1921 and, reverting to the rank of captain in 1920, he was instructor in the department of chemistry at the United States Military Academy from 1921 to 1925. He graduated from the company officer course at the United States Army Infantry School at Fort Benning, Georgia in 1926, and from the advanced course at the United States Army Field Artillery School at Fort Sill, Oklahoma the year after. He was an instructor in weapons and tactics at the United States Army Infantry School from 1927 to 1931 and, promoted to major in August 1932, was executive officer of the 23rd Brigade in Manila, and assistant chief of staff, as a G-2 staff officer, with the Philippine Division from 1933–1934. Collins graduated from the United States Army Industrial College in 1937, and the United States Army War College the following year. He was then an instructor at the Army War College from 1938 to 1940. He was promoted to lieutenant colonel on June 25, 1940 and, now a full colonel (having been promoted on January 15, 1941), was chief of staff of VII Corps in 1941. World War II By the time the United States entered World War II in December 1941, Collins had been a temporary colonel since January. On February 14, 1942 he was promoted to the one-star general officer rank of brigadier general and the two-star general officer rank of major general on May 26. Collins was chief of staff of the Hawaiian Department from 1941 to 1942 and served as the Commanding General of the 25th Infantry Division—nicknamed the "Tropic Lightning" Division—on Oahu and in operations against the Japanese on Guadalcanal between 1942 and 1943 and on New Georgia in from July to October 1943. At the time of his appointment he was the youngest division commander in the United States Army, aged 46. It was during this campaign that Collins gained his nickname of "Lightning Joe". It was also during