Military Sergeants. a rank used in many armies, police forces, and other uniformed organizations. Its origins are in the Latin serviens, "one who serves", through the French term sergent. In most armies the rank of sergeant corresponds to command of a squad (or section). In Commonwealth armies, it is a more senior rank, corresponding roughly to a platoon second-in-command. In the United States Army, sergeant is a more junior rank corresponding to a four-man fireteam leader.