In 1919, he became an aide-de-camp to General Pershing. Between 1920 and 1924, while Pershing was Army Chief of Staff, Marshall worked in a number of positions in the army, focusing on training and teaching modern, mechanized warfare. Between the World Wars, he was a key planner and writer in the War Department, commanded the 15th Infantry Regiment for three years in China, where he learned to speak basic Mandarin. He taught at the Army War College. In 1927, as a lieutenant colonel, he was appointed assistant commandant of the Infantry School at Fort Benning, where he initiated major changes to modernize command and staff processes, which proved to be of major benefit during World War II. Marshall placed Edwin F. Harding in charge of the Infantry School's publications, and Harding became editor of "Infantry in Battle", a book that codified the lessons of World War I. "Infantry in Battle" is still used as an officer's training manual in the Infantry Officer's Course and was the training manual for most of the infantry officers and leaders of World War II.