Senior Airman John Luong, 28th Munitions Squadron munitions inspector, spray-paints a weapon serial number on a bomb dummy unit-50 during a training session at Ellsworth Air Force Base, S.D., Jan. 19, 2016. The WSN is used to label munitions from different pallets so if there was a malfunction it could be easier to determine if it was a technical error or factory issue. (U.S. Air Force photo by Airman 1st Class Denise M. Nevins/Released)