U.S. Army Reserve firefighters with the 468th Engineer Detachment, Danvers, Massachusetts, prepare to descend into a train during a derailment exercise, part of Guardian Response 17 at Muscatatuck Urban Training Center, Butlerville, Indiana, May 7, 2017. Nearly 4,100 Soldiers from across the country are participating in Guardian Response 17, a multi-component training exercise to validate U.S. Army units’ ability to support the Defense Support of Civil Authorities (DSCA) in the event of a Chemical, Biological, Radiological, and Nuclear (CBRN) catastrophe.