The other major factor in the decline of coal was the massive under-investment in Welsh mines over the past decades. Most of the mines in the valleys were sunk between the 1850s and 1880s, so they were far smaller than most modern mines. The Welsh mines were comparatively antiquated, with methods of ventilation, coal-preparation and power supply all of a decades-earlier standard. In 1945 the British coal industry as a whole cut 72% of its output mechanically, whereas in the south of Wales the figure was just 22%. The only way to ensure the financial survival of the mines in the valleys was massive investment from the National Coal Board, but the "Plan for Coal" drawn up in 1950 was overly optimistic about the future demand for coal, which was drastically reduced following an industrial recession in 1956 and an increased availability of oil. From 15,000 miners in 1947, Rhondda had just a single pit within the valleys producing coal in 1984, located at Maerdy.