U.S. Navy seaman-to-admiral 21 (STA-21) and Officer Candidate School are officer candidates (OC). US "Enlisted" and UK "Other ranks" compared UK and US ranks are categorised in the NATO rank code system OR-1 to OR-9. Ranks with the same code are not necessarily equivalent however. Within the US military, however, "E-1" to "E-9" is the more common usage. Notes on comparison: In the US Army OR-1 to OR-4 (specialist) are junior enlisted, OR-4 (corporal) to OR-6 are junior non-commissioned officers (NCOs), and OR-7 to OR-9 are senior non-commissioned officers (SNCOs). In the USAF OR-1 to OR-4 are junior enlisted, OR-5 to OR-6 are NCOs, and OR-7 to OR-9 are SNCOs. In the USMC, OR-1 to OR-3 are junior enlisted, OR-4 to OR-5 are NCOs, and OR-6 to OR-9 are staff non-commissioned officers. In the US Navy and Coast Guard, OR-1 to OR-3 or "nonrated (wo)men" are junior enlisted, OR-4 to OR-6 or petty officers are NCOs, and OR-7 to OR-9 or chief petty officers are SNCOs. In the British Army OR-1 to OR-2 are junior enlisted, OR-3 to OR-4 are junior NCO's, and OR-5 to OR-9 are SNCO's Generally speaking, the RN assumes a rank up despite the NATO code remaining the same. For example, a LH is more practically comparable to a PO2 or PO1 in the USN. While in the British Army a lance corporal is the next rank up from a private, unlike in the US Army they are considered junior NCO's, and hold a similar command appointment to a US Army sergeant. Because of this it is not unheard of for lance corporals to be given US Army sergeant rank insignia when serving with US forces. While there are different pay-grades for privates (and other enlisted ranks) in the British Army, these are tied to job-role (MOS) rather than time in service. As such there is no promotion from a class 4 private to a class 3 private, nor are there differing badges of rank. Addendum: In the US Army (but not the USMC) the term "trooper/(troop)" may be used informally for lower enlisted in cavalry, scout, airborne, air assault, Ranger, and Special Forces units, along with the occasional use for any soldier, particularly dismounted infantry. The specific definition of "troop" is a company-sized unit of cavalry, organizationally equivalent to "battery" in artillery units. Notes to tables above A warrant officer in UK service is a