U.S. ARMY WHITE BIB SCARF

The only place that the white scarf is mentioned in DA 670-1, Guide to the Wear and Appearance of Army Uniforms and Insignia, is in the section devoted to the Ceremonial Blue Overcoat (CBO)—and none of the instructions in that section explain precisely how the scarf is to be worn. Indeed, rather than stating that the white scarf should be worn with the CBO, the manual says that the “CBO…should be worn with the white scarf.”

An optional purchase item, the CBO is authorized for wear by both male and female General Officers and their aides-de-camp, their Command Sergeant Major, and their enlisted aides. When General Officers are reassigned, they and their CSMS retain the overcoat, but their aides-de-camp and enlisted aides are required to turn in their CBOs to the central issuing facility.

The Ceremonial Blue Overcoat with white scarf is worn only on formal ceremonial occasions when (a) cold temperatures demand more protection from the elements than the Army Service Uniform coat can reasonably provide, and (b) the standard black all-weather coat is not suitable for the formality or solemnity of the occasion. Shoulder straps are worn on the CBO, and the Army Service Uniform coat may not be worn under the CBO.
Although it is not mentioned in the any of the typical uniform regulation documents, the white scarf may be prescribed for wear by members of special units such as The Old Guard or the U.S. Army Band because their commanders prescribe the wear policy for all “distinctive uniform items and accouterments.”

Aside from that caveat, the best way to think of the CBO and the white scarf is as the conjoined twins of the Army uniform world: you should never see one without seeing the other.