U.S. Army Reserve Soldiers from the 391st Mobile Augmentation Company (MAC), Boise, Idaho, build a “frag fence,” used to mark the placement of a mine field, during their rotation at the National Training Center (NTC), Fort Irwin, California, January 23, 2019. The 391st took part in the third rotation of NTC for 2019, a training exercise that occurs 11 times per year over the course of 14 days (U.S. Army photo by Sgt. 1st Class Jason Proseus/416th Theater Engineer Command).