SAN DIEGO (Feb. 5, 2021) Master-at-Arms 2nd class Tracer Spurlock, from Murfreesboro, Tenn., clears a hallway during an active shooter drill conducted during exercise Citadel Shield-Solid Curtain 2021 (CS-SC 21). CS-SC 21 is a two-part, force protection exercise that is conducted on installations Navy-wide and is used to evaluate the readiness of fleet and installation security programs. (U.S. Navy photo by Mass Communication Specialist 2nd Class Austin Haist)