(W) and Potsdam Griebnitzsee railway station (E). All transit trains would start or end in East Berlin, passing through West Berlin with only one stop in the Western Berlin Zoologischer Garten railway station, which became West Berlin's main railway station. Until 1952, the Reichsbahn also permitted stops at other stations on the way through the Western sectors. After easing of tensions between East and West Germany, starting on 30 May 1976 transit trains going westwards, southwestwards, or southwards stopped once again at Wannsee. For transit trains going northwestwards, a shorter line was reopened on 26 September 1976 with an additional stop at the then Berlin-Spandau railway station, entering East Germany at Staaken. Many Reichsbahn employees working in West Berlin were West Berliners. Their East German employer, whose proceeds from ticket sales for Western Deutsche Marks contributed to East Germany's foreign revenues, tried to hold down wage social security contributions in Western Deutsche Mark. Therefore, West Berlin employees of the Reichsbahn were paid partly in Eastern German currency. They could spend this money in East Germany and take their purchases to West Berlin, which other Westerners could not do to the same extent. West Berlin employees were trained in East Germany and employed under East German labour laws. West Berliners employed by the Reichsbahn were not included in the Western health insurance system either. The Reichsbahn ran its own hospital for them in West Berlin, the building of which is now used as the headquarters of Bombardier Transportation. For certain patients, the Reichsbahn would facilitate treatment in a hospital in East Berlin. In medical emergencies, the employees could use West Berlin doctors and hospitals, which would then be paid for by the Reichsbahn. The GDR used the western stations to distribute propaganda and display posters with slogans like "Americans Go Home." On 1 May, May Day, a state holiday in East and West, S-Bahn trains were sometimes decorated with the East German banner and a red flag. Waterways Two waterways via the rivers and canals Havel and Mittellandkanal were open for inland navigation, but only freight vessels were allowed to cross from West Berlin into East German waters. The Havel crossed at the East German border in Nedlitz (a part of Potsdam-Bornstedt), continuing through the Elbe-Havel Canal and then either taking the Elbe northwestwards crossing the border again at Cumlosen (E)/Schnackenburg (W) or westwards following the Mittellandkanal to Buchhorst (Oebisfelde) (E)/Rühen