Fortified Railroad Bridge Across Cumberland River, Nashville, Tennessee, 1864

Confederate guerrilla forces, often operating as regular cavalry units, attacked Union-controlled railroad lines. They shot into trains, destroyed tracks, took prisoners, killed Union soldiers, and burned bridges. Union commanders responded by developing block houses and fortified bridges to protect the vulnerable lines, equipping trains with special armor, recruiting loyal local citizens to ferret out guerrillas, and dispatching special counterinsurgency cavalry units to track down the Confederate guerrillas.