<P> The next series of changes to Air Force enlisted ranks did not occur for almost eight years . In January 1967 the position of Chief Master Sergeant of the Air Force was created . This position gained its own special insignia, the Chief Master Sergeant chevrons with a wreath encircling the center star . On 1 August 1967 the lower enlisted rank names changed (revised AFR 39 - 36 on 19 October 1967) renamed Airman Third Class, Airman Second Class and Airman First Class to Airman, Airman First Class and Sergeant (known unofficially as "Buck Sergeant" by the NCO ranks at the time) respectively . This returned Sergeant to the rank structure as the first step in the NCO tier as a retention move but required achievement of a 5 - skill Air Force Specialty Code (AFSC) level . No changes to the respective insignias were made . Footnote: On 1 July 1969 the Air Force Serial Number was changed to the member's Social Security Number (SSAN). This change was for all grades and the three major US military forces including guard and reserve components . The commandant of the USMC did not adopt the serial number change to his forces . </P> <P> In a 30 December 1975 directive the grade of Sergeant was split into two separate ranks while retaining the grade of E-4 . Senior Airman would be the last junior enlisted tier rank while Sergeant would remain the first rank in the NCO tier . The impetus behind this was to laterally promote senior E-4 airmen who were ready for NCO responsibilities but not prepared to take on the role of a Staff Sergeant . This permitted airmen who had not yet reached the AFSC 5 - skill level to achieve the pay grade of E-4, while according those who had NCO status . To differentiate the two ranks, the directive changed the silver star in the center of Airman, Airman First Class and Senior Airman changed to blue while the star on Sergeant chevrons remained silver . Having two ranks within one grade mirrored the Army's Specialist / Corporal division of E-4 . This dual role would last until March 1991 when then Chief of Staff General McPeak terminated the rank of Sergeant effective 2 May 1991 . This termination was due in part to the manning reductions that occurred in the post--Cold War drawdowns of the early 1990s . The last of the "Buck Sergeants" would have either been promoted or discharged under High Year Tenure by December 1998 . </P> <P> The year 1991 also saw the last major change to the enlisted rank insignia . In October 1991 General McPeak and Chief Master Sergeant of the Air Force Pfingston announced that the senior NCO tier would have new chevron layouts and that all chevrons would have a white star in the center . The change in senior NCO chevrons was the first since chevrons came into being in 1948 . Until that time, Master Sergeant had been composed of six inverted chevrons (six down) with none pointing up, Senior Master Sergeant six down with one up and Chief Master Sergeant six down with two up . The new layout changed the insignia to the current layout (see chart above). The second change, changing the star color to white, was actually two changes in one . It added a star to the Airman through Senior Airman rank insignias where there had been none since 1975 (the blue star carried by these chevrons was the same color as the blue in the stripes giving the impression that the star was not there) and changing the silver star on the NCO and senior NCO chevrons to white . </P> <P> In November 1998, the duty position of Senior Enlisted Advisor was changed to Command Chief Master Sergeant . Along with the change, the addition of a star in the empty blue area between the chevrons was added to denote those holding this position . </P>

When did air force master sergeant stripes change