Airman - First Class Airman First Class (A1C) is the third enlisted rank (E-3) in the United States Air Force. The rank of Airman First Class is considered a junior enlisted rank. Senior Airman Senior Airman (SrA) is the fourth enlisted rank in the United States Air Force, just above Airman. The Air Force promotes an Airman First Class (A1C) to Senior Airman after 36 months time in service (TIS) and 20 months time in grade (TIG), or 28 months TIG, whichever occurs first. Outstanding Airmen First Class, limited to no more than 15 percent of the total, may be promoted to Senior Airmen six months early. Technical Sergeant Technical sergeant, "tech sgt" in informal parlance, is the sixth enlisted rank in the U.S. Air Force. A technical sergeant is a noncommissioned officer and abbreviated as TSgt (with no period in official USAF and other military correspondence). Official terms of address are "technical sergeant" or "sergeant", although many use "tech sergeant" in informal situations. Within air force enlisted ranks, promotion to technical sergeant has historically been the second-most difficult rank to achieve. First Sergeant In the United States Air Force, first sergeant is not a rank, but a special duty held by a senior enlisted member of a military unit who reports directly to the unit commander. Often referred to as the "first shirt", or "shirt", the first sergeant is responsible for the morale, welfare, and conduct of all the enlisted members in a squadron and is the chief adviser to the squadron commander concerning the enlisted force. Senior Master Sergeant Promotion to senior master sergeant is the most difficult enlisted promotion to attain in the Air Force. Senior master sergeant (SMSgt) is the eighth enlisted rank in the U.S. Air Force. SMSgts are key, experienced, operational leaders, skilled at merging their personnel's talents, skills, and resources with other teams' functions to most effectively accomplish the mission. SMSgts continue to develop their leadership and management skills in preparation for expanded responsibilities and higher leadership positions. SMSgts normally operate at the operational level of leadership. U.S. Air Force The United States Air Force (USAF) is the aerial warfare service branch of the United States Armed Forces and one of the seven American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on 18 September 1947 under the National Security Act of 1947.