Each branch of the U.S. military uses the same grade system for classifying servicemembers, though the names and titles in use vary according to branch. Enlisted ranks are designated with an "E," followed by the grade, e.g. E-1 and E-2. Warrant officers and line officers' ranks follow the same pattern.
Each service has its own names for the ranks that correspond to the standard grade designations. Enlisted ranks in the U.S. Army, for example, run from Private to Corporal to Sergeant. Each rank is subdivided, so that an army E-1 is a Private, an E-3 is a Private First Class, an E-4 is a Corporal, and the remaining six enlisted grades are all Sergeants. Warrant officers are designated W-1 through W-4, and officers' ranks include Lieutenant, Captain, Major, Colonel and General. Some officer ranks, such as Lieutenant Colonel, are subdivisions of existing ranks. Specialists rate E-4 and are intermediate between Privates and Corporals.
The Marine Corps follows the Army pattern closely, but with minor differences. The Marine rank corresponding to an Army Private First Class is a Lance Corporal, for example.
The Air Force rates all enlisted personnel as Airmen, with subdivisions running from E-1 to E-4. Above that grade, noncommissioned officers are known as Sergeants. Air Force officer ranks are substantially identical to their Army counterparts.
The U.S. Navy has distinct names for almost every rank. E-4 and below are Seamen, while E-5 and above are Petty Officers. Commissioned ranks include Ensign, Lieutenant, Commander, Captain and Admiral. The Coast Guard uses a similar system.