flee this way in Danish ports that harbourmasters installed extra life-saving equipment on quaysides where East German vessels docked. The GDR's government responded by stationing armed Transportpolizei (Trapos) on passenger ships to deal forcefully with escape attempts. On one occasion in August 1961, the Trapos caused an international incident in the Danish port of Gedser, when they beat up a would-be escapee on the quayside and opened fire, hitting a Danish boat in the harbour. The next day, thousands of Danes turned out to protest against "Vopo (Volkspolizei) methods." The "boat-jumpers" were eventually stopped by further restricting the already limited travel rights of the GDR's population. River borders The border also ran along part of the length of three major rivers of central Germany: the Elbe between Lauenburg and Schnackenburg (around ), the Werra and the Saale. The river borders were especially problematic; although the Western Allies and West Germany held that the demarcation line ran along the eastern bank, the East Germans and Soviets insisted that it was located in the middle of the river (the Thalweg principle). In practice, the waterways were shared 50/50 but the navigation channels often strayed across the line. This led to tense confrontations as East or West German vessels sought to assert their right to free passage on the waterways. The rivers were as heavily guarded as other parts of the border. On the Elbe, East Germany maintained a fleet of about 30 fast patrol boats and West Germany had some sixteen customs vessels. The river border was closely watched for escapees, many of whom drowned attempting to cross. Numerous bridges blown up in the closing days of the Second World War remained in ruins, while other surviving bridges were blocked or demolished on the East German side. There were no ferry crossings and river barges were rigorously inspected by the GDR border guards. To prevent escape attempts, the East German river banks were barricaded with a continuous line of metal fences and concrete walls. At one location, Rüterberg on the Elbe, the border fortifications completely surrounded the village and sealed off the inhabitants from the rest of East Germany as well as the West. Border guards of the inner German border The guards of the inner German border comprised tens of thousands of military, paramilitary and civilian personnel from both East and West Germany, as well as from the United Kingdom, the