Having, I believe, started this thread, I want to thank those who have enlightened me on the history, semantics, and the modern usage in the USMC. You've really added to my education. My original query arose from 1860s US and CS army regulations, where the term appeared in the context of the recruiting service of the two armies. What I have gotten from the responses persuades me that, as used in recruiting (or, specifically, in my interest, in the law establishing the CS Signal Corps) it was a provision for temporary exercise of the rank outside of legal billet restrictions--no additional pay, bestowed by the officer-in-charge, possibly marked by temporary wearing of stripes, used to recognize talent or compensate for lack of a sergeant. That understanding fits the circumstances that I faced and clarifies why a man not accounted for officially as sergeant could have been given that temporary rank. A "poor man's brevet."
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