All the branches of the US military have both Officers and Enlisted. Most Enlisted people with a rank of E-4 and above are called Non-commissioned Officers (NCOs); the exception is the Air Force where E-5 is considered the first NCO rank. Their usual duties are to supervise or make sure that common jobs are done properly every day. Most branches also includes "Warrant Officers" ("Chief Warrant Officers" in the Navy.) They are considered experts in their field, they are higher rank than other enlisted troops, but below officers. There are four ranks of Warrant Officers: WO-1 through WO-4 (CWO-1 to CWO-4)