Following the invasion of Poland in September 1939 Nazi Germany disbanded the Polish State Railways (PKP). Polish rail officials were either executed in mass shootings or imprisoned, and some 8,000 managerial positions were staffed with German officials. Former Polish companies began producing German engines BR44, BR50 and BR86 as early as 1940, some using forced labor. By 1944, the factories in Poznań and Chrzanów were producing the redesigned "Kriegslok" BR52 locomotives for the Eastern Front. These locomotives were made almost entirely of steel; the use of more expensive, non-ferrous metals was dropped in view of the engines' expected lifespan. After the war, some 1,200 class 52s remained in reconstituted Poland. Another 200 were acquired from the Soviet Union in 1962–64. The class 52, designated Ty2, began to be phased out in the 1980s; its last regular use was in 1999.