Final answer:
In 1959, the Army NCO ranks added the pay grades of E-8 and E-9 to better delineate responsibilities within their structure, similar to the civil service General Schedule that uses grades and steps to structure pay and responsibilities.
Step-by-step explanation:
The two new pay grades added in 1959 to the Army NCO ranks to provide for a better delineation of responsibilities in the enlisted structure were the grades of E-8 and E-9. These pay grades were introduced to create a clearer hierarchy and designate more specific roles within the non-commissioned officer (NCO) corps. Before 1959, the Army NCO ranks had fewer pay grades, which sometimes led to overlap in responsibilities and a less organized command structure.
The concept of a structured pay grade system is not unique to military service as it is also used in the U.S. federal civil service, where the General Schedule (GS) is utilized. In the General Schedule, there are fifteen grades, each with ten steps, which reflect different levels of required education, competencies, skills, and experiences for civil service positions. Much like the military, civil service positions have a delineated hierarchy based on these structured pay grades, thus allowing a clear path for career growth and responsibility delineation.