<P> Shortly following establishment of the E-8 and E-9 grades, service limits currently known as High Year Tenure (HYT) were established by pay grade . Although these limits periodically flex based on Fleet manpower requirements, current HYT limits restrict Chief Petty Officers not selected for promotion to Senior Chief Petty Officer to 24 years of service, after which they face mandatory retirement . </P> <P> Similar limits of 26 years for Senior Chief Petty Officers and 30 years for Master Chief Petty Officer are currently used, with a smaller core of Master Chief Petty Officers serving in Command, Force or Fleet Master Chief Petty Officer positions in the Navy and Area or the Coast Guard Reserve Force Master Chief in the Coast Guard, being eligible to remain in uniform for 32 to 35 years and with the Master Chief Petty Officer of the Navy and the Master Chief Petty Officer of the Coast Guard being permitted to remain in uniform until reaching 38 years of service . </P> <P> Navy chief petty officers serve a dual role as both technical experts and as leaders, with the emphasis being more on leadership as they progress through the CPO paygrades . A recognized collateral duty for all Chiefs is the training of newly - commissioned junior officers . Like petty officers, every chief petty officer has both a rate (unlike the land - centric services, rank only refers to commissioned officers in the U.S. Navy and U.S. Coast Guard) and a rating (i.e., job specialty, similar to an MOS in the U.S. Army or U.S. Marine Corps, or an AFSC in U.S. Air Force). A chief petty officer's full title is a combination of the two . Thus, a chief petty officer who has the rating of gunner's mate would be referred to as a chief gunner's mate . </P> <P> Each rating has an official abbreviation, such as QM for quartermaster, BM for boatswain's mate, or FC for fire controlman . When combined with the petty officer level, this gives the shorthand for the chief's rate, such as BMC for Chief Boatswain's Mate . It is not uncommon practice to refer to the chief by this shorthand in all but the most formal correspondence (such as printing and inscription on awards). Usually Chief Petty Officers are referred to as "chief", regardless of their rating . </P>

When was the rank of senior chief established