Arthur B. Crean was a master sergeant in the United States Army during World War I. Master Sergeant Crean holds the distinction of being the first ever United States armed forces member to be issued a service number and thus holds service #1 in the United States Army.
Crean enlisted the United States Army in 1899 and by the outbreak of the First World War was part of the enlisted cadre who formed the core of the National Army. In 1920, Crean became one the most senior enlisted members of the peacetime Regular Army.
Crean's service record was destroyed in the 1973 National Archives Fire but a pay record did survive listing some of his service information. Crean is listed in his pay record as being a medical sergeant and the only confirmed military decoration awarded to Crean was the World War I Victory Medal.
In June 1921, when John Pershing was listed as holding the first officer service number (O-1), Crean's service number was slightly modified. His new number became "R-1" to denote Regular Army #1.