MCPO meaning in Governmental ?

Master chief petty officer (MCPO) is an enlisted rank in some navies. It is the ninth, (just below the rank of MCPON) enlisted rank (with pay grade E-9) in the United States Navy and United States Coast Guard, just above command senior chief petty officer (CMDCS). Master chief petty officers are addressed as "Master Chief (last name)" in colloquial contexts and they constitute the top 1.25% of the enlisted members of the maritime forces.

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.