There was a significant demand for building materials after the First World War, as Britain recovered from the conflict and many new houses were built to replace slums. The slate industry had been largely mothballed during the conflict, but now found itself in a boom period. Shortly after the war, the quarry began producing Fullersite - ground slate waste - which was shipped in large quantities along the railway. In 1924, with traffic continuing the rise, three additional Baldwin locomotives were purchased. These had been built for war use by the United States Army Transport Corp, and were refurbished before being sold to the railway, but were not successful, and after three years of intermittent use they were put aside.