Northwest quadrant of a U.S. military topographic map covering karst terrain near Ban Senphan, Laos, part of the reference materials associated with the 'Boxer 22' combat search-and-rescue operation during the Vietnam War. Maps like this one were used by rescue coordinators and aircrews to plan routes through the rugged, cave-riddled limestone terrain of the Ho Chi Minh Trail corridor while attempting to locate and recover downed American airmen. Project: 218834