In May 1942, five Polish students of the Salesian Oratory in Poznań, known as the "" or five of the 108 Blessed Polish Martyrs of World War II, were imprisoned in Zwickau, before being executed in Dresden. A subcamp of the Flossenbürg concentration camp was located in Zwickau, whose prisoners were mostly Poles and Russians, but also Italians, French, Hungarians, Jews, Czechs, Germans and others. On 17 April 1945, US troops entered the city. They withdrew on 30 June 1945 and handed Zwickau to the Soviet Red Army. Between 1944 and 2003, the city had a population of over 100,000. A major employer is Volkswagen which assembles its Golf, Passat and Phaeton models in the Zwickau-Mosel vehicle plant. Coal mining is mentioned as early as 1348. However, mining on an industrial scale first started in the early 19th century. The coal mines of Zwickau and the neighbouring Oelsnitz-Lugau coalfield contributed significantly to the industrialisation of the region and the town. In 1885 Carl Wolf invented an improved gas-detecting safety mining-lamp. He held the first world patent for it. Together with his business partner Friemann he founded the "Friemann & Wolf" factory. Coal mining ceased in 1978. About 230 million tonnes had been mined to a depth of over 1,000 metres. In 1992 Zwickau's last coke oven plant was closed. Many industrial branches developed in the town in the wake of the coal mining industry: mining equipment, iron and steel works, textile, machinery in addition to chemical, porcelain, paper, glass, dyestuffs, wire goods, tinware, stockings, and curtains. There were also steam saw-mills, diamond and glass polishing works, iron-foundries, and breweries. In 1904 the Horch automobile plant was founded, followed by the Audi factory in 1909. In 1932 both brands were incorporated into Auto Union but retained their independent trademarks. The Auto Union racing cars, developed by Ferdinand Porsche and Robert Eberan von Eberhorst, driven by Bernd Rosemeyer, Hans Stuck, Tazio Nuvolari, Ernst von Delius, became well known all over the world. During World War II, the Nazi government operated a satellite camp of the Flossenbürg concentration camp in Zwickau which was sited near the Horch Auto Union plant.