200204-N-SK941-0009 GREAT LAKES, Ill. (Feb. 4, 2020) Sailors respond to a simulated active shooter scenario during a drill a part of Exercise Citadel Shield-Solid Curtain 2020. Exercise Citadel Shield-Solid Curtain 2020 is a two-part, anti-terrorism force protection exercise that is being conducted nationwide on Navy installations, Feb. 3-14. The annual exercise is not in response to any specific threat, but is used to evaluate the readiness of the fleet and installation security. (U.S. Navy photo by Quartermaster 2nd Class Kevin Hopkins/Released)