Just got this S/N C74820=1943 U.S.Govt on movement

most.

C74820

case back

Below are what the various U.S. Army Ordnance Deparment codes mean:

OA - 7 to 9 jewel pocket watches
OB - 15 to 17 jewel pocket watches
OC - 7 to 9 jewel wristwatches
OD - 15 to 17 jewel wristwatches
OE - 21 jewel railroad grade pocket watches
OF - 15 to 17 jewel wristwatches with waterproof case
OFA - 15 to 17 jewel wristwatches with waterproof case, Air Corps (Navigation, Type A-11, substitute standard)
OG - 7 to 9 jewel wristwatches (waterproof cases)
OS - stopwatch
OW - 7 to 9 jewel pocket watches made before Nov. 12, 1940 and remarked later
OX - 15 to 17 jewel pocket watches made before Nov. 12, 1940 and remarked later
OY - 7 to 9 jewel wristwatches made before Nov. 12, 1940 and remarked later
OZ - 15 to 17 jewel wristwatches made before Nov. 12, 1940 and remarked later