Master Sgt. Nathan Landry, the first sergeant assigned to the 28th Medical Group, and Master Sgt. Luis Guillen-Diaz, the mental health flight chief and additional-duty first sergeant assigned to the 28th MDG, join Staff Sgt. Ricky Dunbar, an education and training noncommissioned officer in charge assigned to the 28th MDG, while he teaches a course on CPR at Ellsworth Air Force Base, S.D., June 9, 2017. Each first sergeant has a handful of additional-duty first sergeants, usually around four or five, ready to drop what they’re doing at moment’s notice to take up the mantel. (U.S. Air Force photo by Airman 1st Class Donald C. Knechtel)