During World War II hostilities in the Baltic Sea commenced on 1 September 1939 when the German battleship Schleswig-Holstein opened fire on the Polish fortress of Westerplatte and ended on 9 May 1945 with the final evacuation of German refugees from the Hela peninsula. In the intervening years battles raged back and forth between the confines of this cold cruel sea. The Soviets attacked the Finnish island of Russar on 30 November 1939 with an air and naval bombardment. The Russian naval blockade of Finland began and their submarines attacked merchant vessels in the Gulf of Bothnia and their ships engaged shore batteries and coastal towns. The German fleet then turned on their former allies and attacked the Soviet Union, each sides submarines stalked the others and the Russians encountered disaster in a minefield. Finally the Russians retreated under heavy sea and air attack. The siege of Leningrad began in September 1941 and was not broken until 1943. In 1944 the Russians reached Riga, leaving pockets of stranded German troops on the Courland Peninsula. Then the Russian navy broke out the race for East Prussia was on, sparking the biggest seaborne evacuation in history.