During the years 1890 to 1925 the valley gained a worldwide reputation as a producer of Admiralty-grade steam coal, high quality coking coal and what was regarded as the best house coal in South Wales. As a measure of the quality of Llynfi Valley steam coal, (North's) "Imperial" "Navigation" coal was included on the prestigious Admiralty List of the twenty–six best Welsh steam coals and, in 1908, the Cunard liner "Mauretania" was entirely fired by Llynfi coal when the ship established a new record for crossing the Atlantic. By the early 1920s there were over 7,000 miners at work in the valley. However, as the area depended to such a large extent on the coal export trade, it was seriously affected by the trade depression of 1928-38. During that period of acute poverty and large-scale unemployment, the population of the Llynfi Valley decreased by almost a third as many left the district to seek employment in the new light industries growing up in areas such as West London and the English Midlands.