During the Civil War, soldiers in the Union Army would be brevetted in a rank and while having the right to be addressed by that rank and even fill the post appropriate to that rank, they retained the pay of their original rank. Thus, one might be a full colonel and brevetted as a brigadier general and command a brigade (about four to five regiments), he would still be a colonel.
Thus it came to pass that mules who performed well were jokingly made brevet horses. Well, here's one that didn't apply to horses:
General Hazen of our corps has been made a full major general. The other divisions commanders only by brevet, and they feel a little sore over it. To-day one of General Wood's aids saw a turkey buzzard, and pointed out to the general, saying, "there is a turkey." Old Woods looked at it and answered, "I think it is a turkey by brevet."