on blue fields for the lower half or upper half, respectively. The flags of restricted line officers and staff corps officers have blue stars on a white field. All services officially list the two-star grade as rear admiral and not rear admiral (upper half) as stated by and of the U.S. Code of law. However, the four uniformed services will sometimes list the rank as rear admiral (upper half) to help the general public distinguish between the two grades. United States Maritime Service Although it exists largely as a maritime training organization, the United States Maritime Service does use the ranks of rear admiral (upper half) and rear admiral (lower half). By law, the Service has the same rank structure as the United States Coast Guard, but its uniforms are more similar to the United States Navy. Statutory limits By statute, Congress has expressly limited 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 as part-time drilling reservists. Some of these billets 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. A newer statute enacted in 2016 lowers the cap on the total number of active duty flag officers in the Department of Defense to 151, effective December 31, 2022. 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. The Coast Guard's chief medical officer is also a commissioned corps two-star rear admiral, on assignment to the Coast Guard. Officers serving in certain intelligence positions are not counted against the statutory limit. Promotion, appointment, and tour length 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