The US Army classified its various uniforms
according to their particular function:
Class A -
Officially known as Service Dress, this was the US serviceman's 'Sunday
best' uniform that he would have worn on parades or out on the town.
Officers' Class A uniform was also known as 'Pinks & Greens'.
Class B -
This was the smart in-barracks working dress and was essentially the
Class A uniform minus its jacket. Sometimes known as 'informal post
Class C -
This was the summer/tropical uniform made of light khaki
woollen-worsted material (officers) or cotton (enlisted men).
Class D -
Fatigue dress made of herringbone twill material. Not usually
applicable to officers