Senior Master Sergeant (SMSgt) is the eighth enlisted rank in the UNSC Air Force, immediately below Chief Master Sergeant/Command CMSgt, and above Master Sergeant. The pay grade for Senior Master Sergeant is E-8, and is a senior Non-commissioned officer rank in the UNSCAF. It is equal to an Army or Marine Corps Master Sergeant or First Sergeant. It is also equal to a Navy Senior Chief Petty Officer.

Promotion to Senior Master Sergeant is the most difficult enlisted promotion to attain in the Air Force. It is the first enlisted grade in which results of a central promotion board are the primary factor in selection for promotion. Usually, less than ten percent of eligible Master Sergeants are selected for promotion to Senior Master Sergeant. Candidates typically have vast technical and leadership experience gained from a broad variety of assignments at both line and staff functions throughout their careers. Additionally, the successful candidate will typically have at the minimum a completed associate's or bachelor's degree in their Air Force specialty as well as the Senior Non-commissioned Officer Correspondence Course, and have had their latest performance report endorsed by a senior rater, usually a Colonel or Brigadier General.

Senior Master Sergeants typically assume superintendent duties, overseeing enlisted members' efforts to accomplish a major segment of a unit's mission, in preparation for promotion to the rank of Chief Master Sergeant. They are expected to serve as mentors for non-commissioned and junior commissioned officers.

Senior Master Sergeants in the First Sergeant special duty serve as First Sergeants of larger units than those employing a Master Sergeant as a First Sergeant. These First Sergeants (pay grades E-7 to E-9) are referred to officially as "First Sergeant" (regardless of their pay grade), and unofficially as "First Shirt" or simply the "Shirt."

Senior Master Sergeants are sometimes referred to by the nickname of "Senior." This usage is an informal one, however, and would not be used in an official or formal setting. The official term of address is "Senior Master Sergeant" or "Sergeant."

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