continues in four of the six branches of the U.S. armed forces. The U.S. Air Force does not allow the regular practice of frocking before a promotion date, except in rare circumstances, such as when an officer selected for promotion is assigned to a billet (typically a senior joint duty assignment), that requires them to hold/wear the higher rank to which they are expected to be promoted. Frocking typically requires special approval to be obtained from the service headquarters. The services differ in how they deal with officers who have been selected for promotion, but not yet promoted, as happens with a promotion list. An Army lieutenant colonel who has been selected for promotion to colonel uses lieutenant colonel (promotable), while in the Air Force, that officer would use colonel (select). The promotion of an enlisted person or non-commissioned officer to commissioned officer rank as a reward for displaying leadership and bravery is referred to as a direct appointment rather than a brevet. It temporarily grants up to the rank of first lieutenant. The holder must then attend Officer Candidate School in order to keep the commission. They must also have or acquire a four-year college degree if they wish to be promoted to the rank of captain or above. The U.S. National Guard, which depends on the governor of a state to concede its commissions in the Army National Guard and Air National Guard, may still confer brevets. Many states maintain a clause permitting the governor to confer any rank in its defense forces, including the militia and National Guards. Some states provide that the sitting governor may confer any rank, but this appointment is considered valid only for the duration of the governor's own term in office. Some states also confer brevets as part of their regular honors system. Georgia confers honorary ranks into its state police force. Kentucky is famous for its colonels, and so too is Tennessee, both of which make the appointment as an honorary member of the governor's staff. Alabama, Kentucky, Texas and Nebraska also confer flag officer ranks within a symbolic navy. Similar honors have been issued for the Georgia Naval Militia, which has existed only on paper since 1908. In all cases these honorary titles may be considered effective brevets, equal to that of the National Guard, by being conferred by a sitting governor. The 2019 John S. McCain National Defense Authorization