Service arm and rank in the army.
USA -- National Army.
U.S.R. -- Reserve Corps.
The above letters, plain for officers and enlisted men, dress uniform as buttons for enlisted men, service uniform, are worn on collar of coat, or on the collar of the skirt if the coat is not worn:
The arms of the services are indicated by service hat cords and by collar insignia.
americans-ww1852
American heavy artillery
americans-ww1924
A flock of fighting English Tanks
americans-ww1933
Barbed wire cut
americans-ww1938
A collection of photographs
americans-ww11769
Yanks going into action, France
americans-ww1697
Yanks in front line Trench
americans-ww1750