ELLSWORTH AIR FORCE BASE S.D. -- (Right to left) Senior Airman Kristi Terwilliger, 28th Security Forces Squadron controller, and Senior Airman Chadwick Richardson, 28 SFS patrol leader, patrol the simulated perimeter during a phase II operational readiness exercise, July 20. Security Forces patrol the simulated deployed base, monitoring for potential threats within the scope of the exercise. (U.S. Air Force photo/Airman 1st Class Anthony Sanchelli)