McRae was commissioned in the Third Infantry and performed frontier duty from 1886-1888. During the Spanish–American War, he was in the Battle of El Caney in Cuba, and he also served in the Sanitary Corps, for which he received his first Silver Star Commendation. He received his second Silver Star during the Philippine Insurrection and was recommended for a brevet promotion. From 1905 to 1908, he served on the General Staff, and in 1911, he graduated from the United States Army War College. McRae served in the Adjutant General's Department from 1913 to 1917, and on August 5, 1917, he was promoted to brigadier general and commanded the 158th Depot Brigade at Camp Sherman, Ohio. In addition, he commanded the Ninth Infantry Brigade of the Fifth Infantry Division. He was promoted to major general on April 12, 1918, and commanded the 78th Infantry Division (AEF) until June 1919, when it was inactivated. For this, he earned the Distinguished Service Medal. During 1921 and 1922, he was assistant chief, G-1 (personnel).