The Lewis Gun was developed by American Isaac Newton Lewis shortly before WWI, but the US military was not interested in it (in part because of a bitter dislike between Lewis and the Chief of Army Ordnance Crozier). Lewis instead licensed production to BSA in England, and the gun because a major part of UK armament during the First World War, both in ground and aerial roles. For a more complete view of the Lewis, check out my previous video on it, with disassembly and shooting.