Kohtla-Järve shale oil combinate (, now Viru Keemia Grupp) under the General Directorate of Synthetic Liquid Fuel and Gas of the USSR (Glavgaztopprom). Both organisations were directed from Moscow. New mines were opened in Ahtme (1948), Jõhvi (No. 2, 1949), Sompa (1949), Tammiku (1951), and in the area between Käva and Sompa (No. 4, 1953). The Küttejõu open-pit mine was closed in 1947 and the Küttejõu underground mine was merged with the Kiviõli mine in 1951. The Ubja mine was closed in 1959. After construction of large oil shale-fired power stations, demand for oil shale increased and consequently new larger mines were constructed: the underground mines Viru (1965) and Estonia (1972) along with the open-pit mines Sirgala (1963), Narva (1970) and Oktoobri (1974; later named Aidu). Correspondingly, several exhausted smaller mines like Kukruse (1967), Käva (1972), No. 2 (1973), No. 4 (1975), and Kiviõli (1987) were closed. The Estonia Mine became the largest oil shale mine in the world. Because of the success of oil shale-based power generation, Estonian oil shale mining peaked in 1980 at 31.35 million tonnes, and in the same year power generation peaked at 18.9 TWh. The industry declined during the subsequent two decades. Demand for electric power generated from oil shale decreased following construction of nuclear power stations in the Russian SFSR, particularly the Leningrad Nuclear Power Station. At the end of 1988, a fire broke out in the Estonia Mine. The largest underground fire in Estonia, it continued for 81 days and caused serious pollution of ground and surface waters. The shale oil industry at Kohtla-Järve and Kiviõli was redeveloped. In 1945, the first tunnel kiln was restored, and by the end of the 1940s four tunnel kilns located in Kiviõli and Kohtla-Nõmme had been restored. German prisoners of war contributed most of the labour. Between 1946 and 1963, 13 Kiviter-type retorts were built in Kohtla-Järve and eight in Kiviõli. In 1947, a pilot Galoter retort was built at the Ilmarine engineering plant in Tallinn. This unit, in operation until 1956, was capable of processing 2.5 tonnes of oil shale per day and was used for modelling the next generation of commercial-scale retorts. The first Galoter-type commercial-scale pilot retorts were built at Kiviõli in 1953 and 1963 with capacities of 200 and 500 tonnes of oil shale per day, respectively. The first of these retorts closed in 1963 and the second in 1981. The