\Serv"ice cap\ or hat \hat\ (Mil.)
A cap or hat worn by officers or enlisted men when full-dress
uniform, or dress uniform, is not worn.

Note: In the United States army the service cap is round,
      about 31/2 inches high, flat-topped, with a visor. The
      service hat is of soft felt of khaki color, with broad
      brim and high crown, creased down the middle.