BUTLERVILLE, Ind. (May 1, 2021) U.S. Army Spc. David Rivas, and Spc. Daniel Schantin, both assigned to the 546th Area Support Medical Company, treat a mock casualty's injuries during exercise Guardian Response 21 (GR 21) at Muscatatuck Urban Training Center, Indiana, May 1, 2021. GR 21 is an annual exercise used to train and evaluate the Department of Defense's chemical, biological, radiological and nuclear (CBRN) response enterprise (CRE). Upon completion of the culminating training event, the CRE allocated units are postured to rapidly deploy to support no-notice CBRN or defense support to civil authorities response operations anywhere in the United States. (U.S. Navy photo by Mass Communication Specialist 2nd Class Michael H. Lehman)