Final answer:
The paygrades for senior chief and master chief petty officer were established in 1958, modernizing the Navy's rank structure and acknowledging the need for senior non-commissioned officers.
Step-by-step explanation:
The paygrades for senior chief and master chief petty officer were established in the year 1958.
The creation of these paygrades (E-8 and E-9, respectively) was part of the Navy's efforts to modernize its rank structure and provide career paths and advancement opportunities for its enlisted personnel. Prior to 1958, the highest enlisted rank was Chief Petty Officer. The establishment of these senior ranks recognized the need for experienced senior non-commissioned officers.