in the early history, the king of france would call on his feudal lords for troops. these feudal lords raised armies and appointed officers, but they did not have the authority to give a rank in the king's army. the king would give a commissioned rank to leaders that would be recognized throughout his army by the use of letters patent or brevet. soon all french officers from a cornet (sub-lieutenant) to the marshal of france received their commission in this way. they came to be styled "officers a'brevet". the official document granting the brevet was called a "brevet d'invention".