Complex sentence: During 1918, the School for Aerial Observers and the Air Service Flying School were built at nearby Post Field, where Walker spent the next four years as a pilot, instructor, supply officer, and post adjutant.
Split into simpler sentences: During 1918, the School for Aerial Observers and the Air Service Flying School were built at nearby Post Field. He remained at Post Field for four years as a pilot, instructor, supply officer, and post adjutant.