<P> Although it exists largely as a maritime training organization, the United States Maritime Service does use the rank of rear admiral (upper half) and rear admiral (lower half). By law, the Service has the same rank structure of the United States Coast Guard, but its uniforms are more similar to the United States Navy . </P> <P> U.S. Code of law explicitly limits the total number of flag officers that may be on active duty at any given time . The total number of active duty flag officers is capped at 162 for the Regular Navy, augmented by a smaller number of additional flag officers in the Navy Reserve who are either on full - time active duty, temporary active duty, or on the Reserve Active Status List (RASL) as part - time drilling reservists . Some of these slots are reserved or set by statute . For example, the Deputy Judge Advocate General of the Navy is a two - star rear admiral in the Navy . In the Coast Guard, the Chief Medical Officer is also two - star rear admiral In the Public Health Service Commissioned Corps, at least half of the Assistant Surgeons General are one - star rear admirals and no more than half are two - star rear admirals . Officers serving in certain intelligence positions are not counted against the statutory limit . </P> <P> For the Navy and the Coast Guard, to be promoted to the permanent grade of rear admiral (lower half) or rear admiral, officers who are eligible for promotion to these ranks are screened by an in - service promotion board composed of other flag officers from their branch of service . This promotion board then generates a list of officers it recommends for promotion to flag rank . This list is then sent to the service secretary and the joint chiefs for review before it can be sent to the President, through the defense secretary for consideration . The president nominates officers to be promoted from this list with the advice of the Secretary of Defense, the service secretary, and if applicable, the service's chief of staff or commandant . The President may nominate any eligible officer who is not on the recommended list if it serves in the interest of the nation, but this is uncommon . The Senate must then confirm the nominee by a majority vote before the officer can be promoted . Once confirmed, a nominee is promoted once he or she assumes an office that requires or allows an officer to hold that rank . For one - star or two - star positions of office that are reserved by statute, the President nominates an officer for appointment to fill that position . For the Navy and the Coast Guard, because the one - star and two - star grades are permanent ranks, the nominee may still be screened by an in - service promotion board to add their input on the nominee before the nomination can be sent to the Senate for approval . For the NOAA Commissioned Officer Corps and the Public Health Service Commissioned Corps, one - star and two - star rank are achieved by appointment from the President, or from their department secretary, and do not require senatorial approval . The standard tour length for most rear admiral positions is three years, but some are set at four or more years by statute . For the Navy, Coast Guards and NOAA Corps, both grades of rear admiral are permanent ranks and do not expire when the officer vacates a one - star or two - star position . The Public Health Service Commissioned Corps, however employs permanent promotions in both grades of rear admiral as well as position - linked temporary appointments in both grades . Their temporary ranks expires when those officers vacate certain temporary positions of office designated to bear those ranks . </P> <P> By tradition in the United States Navy, when an officer is selected or appointed to flag rank, all current Navy flag officers write the selectee a letter congratulating him or her for attaining flag officer status . </P>

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