From the 17th century in Maryland until the late 1990's, tobacco was the agricultural mainstay in Southern Maryland, and tobacco barns were essential to that economy because they were built to air-cure tobacco plants inside, using many exterior ventilation doors to circulate air through interior "rooms." The 2001 Maryland Tobacco Buyout effectively ended tobacco's reign as Southern Maryland's main cash crop by offering voluntary funds to growers who chose to stop growing tobacco while remaining in agriculture. Since then, disuse and urban sprawl have placed the barns at risk, and although they are quickly vanishing, they are receiving conservation attention as an essential part of Maryland's farming history. By 1952, the Navy operated three diesel locomotives on 55 miles of track, with an average of 110 cars running weekly between Brandywine and Patuxent River, but this busy period was short-lived, and by 1953 the Navy chose to discontinue rail service in favor of roadway, air, and water transportation.