<P> Master chief petty officer (MCPO) is the ninth, and highest, enlisted rate (pay grade E-9) in the United States Navy and United States Coast Guard, just above senior chief petty officer (SCPO). Master chief petty officers are addressed as "Master Chief (last name)" in the colloquial and they constitute the top 1.25% of the enlisted members of the maritime forces . </P> <P> Prior to 1958, chief petty officer was the highest enlisted rate in both the U.S. Navy and U.S. Coast Guard . This changed on 20 May 1958 with the passage of Public Law 85 - 422, the Military Pay Act of 1958, which established two new enlisted pay grades of E-8 and E-9 in all five branches of the U.S. Armed Forces . In the U.S. Navy and U.S. Coast Guard, the new E-8 pay grade was titled Senior Chief Petty Officer and the new E-9 pay grade as Master Chief Petty Officer, with the first selectees promoting to their respective grades in 1959 and 1960 . </P> <P> In the Navy, advancement to master chief petty officer is similar to that of chief petty officer and senior chief petty officer . It carries requirements of time in service, superior evaluation scores, and selection by a board of master chiefs . Similarly, senior chief petty officers and chief petty officers are chosen by selection boards . In the Coast Guard, advancement to master chief petty officer is similar to other advancements consisting of competition with other advancement - eligible senior chief petty officers . Eligible candidates are prioritized based on written examination scores, evaluations, award points, time in service, and time in grade . Master chief petty officers are then selected monthly from this prioritization list as positions become available . </P>

When was the rank of senior and master chief petty officer established