Narva Oil Plant, annexed to the Eesti Power Station and operating two Galoter-type 3,000-tonnes-per day retorts, was commissioned in 1980. Started as a pilot plant, the process of converting it to a commercial-scale plant took about 20 years. In 1948 an oil shale gas plant in Kohtla-Järve became operational, and for several decades the oil shale gas was used as a substitute for natural gas in Saint Petersburg (then known as Leningrad) and in northern Estonian cities. It was the first time in history that synthetic gas from oil shale was used in households. To enable delivery of the gas, a pipeline from Kohtla-Järve to Saint Peterburg was built, followed by a pipeline from Kohtla-Järve to Tallinn. During the 1950s, unsuccessful tests of oil shale underground gasification were conducted at Kiviõli. In 1962 and 1963, the conversion of oil shale gas into ammonium was tested; however, for industrial production, oil shale gas was replaced with natural gas. Although this gas had become uneconomical by 1958, production continued and was even expanded. After peaking in 1976 at , oil shale gas production ceased in 1987. In total, 276 generators were operated for the gas production. In 1949, the 48 MW Kohtla-Järve Power Station – the first power station in the world to use pulverised oil shale at an industrial scale – was commissioned, followed by the 72.5 MW Ahtme Power Station in 1951. To ensure sufficient electricity supply in Estonia, Latvia and north-west Russia, the Balti Power Station (1,430 MW) and the Eesti Power Station (1,610 MW) were built, the former between 1959 and 1971 and the latter between 1969 and 1973. The stations, collectively known as the Narva Power Stations, are the world's two largest oil shale-fired power stations. In 1988 Moscow-based authorities planned a third oil shale-fired power station in Narva with a capacity of 2,500 MW, together with a new mine at Kuremäe. The plan, disclosed at the time of the Phosphorite War and the Singing Revolution, met with strong local opposition and was never implemented. Between 1946 and 1952, uranium compounds were extracted from locally mined graptolitic argillite at the Sillamäe Processing Plant (now: Silmet). More than 60 tonnes of uranium compounds (corresponding to 22.5 tonnes of elemental uranium) were produced. Some sources note that uranium produced in Sillamäe was used for construction of the first Soviet atomic bomb; however, this information is not confirmed by the