In the United States Armed Forces, the rank of warrant officer (grade W-1 to CW-5) (NATO: WO1-WO5) is rated as an officer above the senior-most enlisted ranks, as well as officer cadets, midshipmen and candidates, but below the officer grade of O-1 (NATO: OF-1). Warrant officers are highly skilled, single-track specialty officers, and while the ranks are authorized by Congress, each branch of the uniformed services selects, manages, and utilizes warrant officers in slightly different ways. For appointment to warrant officer one (W-1), a warrant is approved by the secretary of the respective service. For chief warrant officer ranks (W-2 to W-5), warrant officers are commissioned by the President of the United States and take the same oath as regular commissioned officers (O-1 to O-10).
While the term 'warrant officer' is used by many military services the world over, the category of officers to which the United States applies the term is unique to the U.S. armed forces. Care should thus be exercised when interpreting the phrase in international contexts. In most other militaries, such as those of the Commonwealth, "warrant officer" refers to NATO OR-8 and OR-9, the equivalent of American master sergeants, senior chief petty officers, sergeants major, and master chief petty officers.
Warrant officers can and do command detachments, units, activities, vessels, aircraft, and armored vehicles as well as lead, coach, train, and counsel subordinates. However, the warrant officer's primary task as a leader is to serve as a technical expert, providing valuable skills, guidance, and expertise to commanders and organizations in their particular field.