of his class included Jacob L. Devers (39th), George S. Patton (46th), and Robert L. Eichelberger (68th), all of whom eventually reached four-star rank, and John C. H. Lee (12th), and Delos C. Emmons (61st), who reached three-star rank. World War I Simpson's first assignment was with the 2nd Battalion, 6th Infantry Regiment, which was stationed at Fort Lincoln, North Dakota. Soon after he joined in the regiment on September 11, 1909, it received orders to deploy to the Philippines. He embarked from San Francisco on January 5, 1910. He went to the island of Mindanao in the Philippines and participated in suppression of the Moro Rebellion. He returned to the United States with his regiment, arriving at the Presidio of San Francisco on July 10, 1912. The regiment moved to El Paso, Texas, between April 24 and May 1, 1914. Promoted to first lieutenant on July 1, 1916, he commanded Companies C and K in the Pancho Villa Expedition in 1916. On February 24, 1917, he became aide-de-camp to Brigadier General George Bell Jr., the commander of the El Paso Military District. Simpson was promoted to captain on May 15, 1917, a month after the American entry into World War I. He followed Bell on a tour of inspection of the British and French forces on the Western Front in September and October 1917. They then returned to Camp Logan, Texas, where the 33rd Division was activated, with Bell, now a major general, as its first commander. The 33rd Division embarked for France on May 16, 1918. Simpson became its Assistant Chief of Staff (G-3), the staff member responsible for operations. He was promoted to major on June 7, 1918, and attended the American Expeditionary Forces (AEF) Army General Staff College from June 15 to August 30. He returned to the 33rd Division as assistant to its G-2 (the staff member responsible for intelligence) on September 1, then became assistant to its G-3 on September 15. He became G-3 again on October 4, and participated in the Meuse–Argonne offensive. He was promoted to lieutenant colonel on November 5, and became the division's chief of staff on November 17, soon after World War I ended on November 11, 1918. For his services during the war he was awarded the Army Distinguished Service Medal and Silver Citation Star, and the French Croix de guerre and Legion of Honour in the grade