The concept of longwall mining in the United States dates back to the late 19th century when wide faces were used for coal extraction in the Pittsburgh seam. But modern, fully mechanized longwall mining employing plows and frame supports was first introduced from West Germany in the early 1950s in southern West Virginia. The growth of US longwall mining production in has been phenomenal. In 1975, there were 76 longwall faces, but their production was a mere 4% of underground coal mining production. According to the 2019 US longwall census, there were 37 active longwall faces producing from slightly more than one million to 7.23 million clean tons of coal in 2018. Most US longwall mines operate one longwall unit in a mine and produce three to seven million clean tons annually, although several mines routinely operate two longwalls units occasionally; a few mines even operated three units in order to either keep up with or increase production.