" Depending on the context, this could refer to a specific military unit, a historical record, or even a technical part number.

"6 YRC" may be a specific shelf mark or reference number in a digital library like the .

This could be a specific Yearly Record Card or a clerical code used in personnel or maintenance archives.

"No. 6 Squadron RAF history 1940s" (or your specific era) For technical info: "RAF YRC part specification" 6 Squadron?