200207-N-AN781-1033 NAVAL BASE SAN DIEGO (Feb. 7, 2020) Sailors from Naval Base San Diego Security Forces engage an active shooter during 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 installations, Feb. 3-14. The annual exercise is not a response to any specific threat, but is used to evaluate the readiness of fleet and installation security programs. (U.S. Navy photo by Mass Communication Specialist 2nd Class William Phillips/Released)