Saltpeter, an essential ingredient in gunpowder, had been mined at Organ Cave since the eighteenth century, but demand rose sharply during the Civil War. Beginning in 1861, Confederate soldiers operated the mine there and eventually produced a large share of the saltpeter used for Confederate gunpowder. Many lived in the cave during severe winters, held religious services in the Chapel Room, and relied on a stream inside the cave for cooking, washing, and drinking. They built fifty-two vats, or hoppers, to separate saltpeter from the surrounding rock and soil, and thirty-seven remain in the Hopper Room as the largest such collection in the United States. Soldiers carried sacks of soil to the hoppers, where water leached out the saltpeter; filling one hopper required an estimated 2,000 pounds of soil hauled in 14-16 trips. After two hundred pounds of saltpeter had been extracted, it was shipped to Southern gunpowder factories such as Augusta, Georgia. On August 19, 1863, Gen. William W. Averell led a cavalry expedition into West Virginia that included Greenbrier County with the goal of destroying saltpeter works in Pendleton County, and although Organ Cave was not attacked, production there apparently ended soon afterward. After the Civil War, Organ Cave resumed its role as a tourist attraction.