In the United States Armed Forces, the ranks of warrant officer (grades W‑1 to W‑5; see NATO: WO1–WO5) are rated as officers above all non-commissioned officers, candidates, cadets, and midshipmen, but subordinate to the lowest officer grade of O‑1 (NATO: OF‑1). This application differs from the Commonwealth of Nations and other militaries, where warrant officers are the most senior of the other ranks (NATO: OR‑8 and OR‑9), equivalent to the U.S. Armed Forces grades of E‑8 and E‑9.
Warrant officers are highly skilled, single-track specialty officers. While the ranks are authorized by Congress, each branch of the uniformed services selects, manages, and uses warrant officers in slightly different ways. For appointment to the rank of warrant officer one (W‑1), normally a warrant is approved by the secretary of the respective service. However, appointment to this rank can come via commission by the service secretary, the department secretary, or by the president, but this is more uncommon. For the chief warrant officer ranks (CW‑2 to CW‑5), these warrant officers are commissioned by the president. Both warrant officers and chief warrant officers take the same oath as regular commissioned officers (O‑1 to O‑10).