Born in Boston, Massachusetts, he initially went to Harvard before securing a place in the Naval Academy. On March 17, 1907, Sumner was commissioned a Second Lieutenant in the Marine Corps. Until 1909 he was stationed in turn at the Marine Barracks of the Naval Academy, Annapolis, Maryland, and Norfolk Navy Yard. He was then ordered to Cuba with the 1st Provisional Regiment of Marines in the Army of Cuban Pacification. In December 1909, he served on temporary duty on the USS Prairie. He retired on January 1, 1914, after seven years service.