Even more important to many Jews was the permission to settle in the British-controlled Mandatory Palestine. In order to try to maintain peace between the Jewish and Arab populations, especially after the 1936–1939 Arab revolt in Palestine, Britain strictly limited immigration. This limitation became nearly absolute after the White Paper of 1939 all but stopped legal immigration. During the War, Zionists organised an illegal immigration effort, conducted by "Hamossad Le'aliyah Bet" (the precursor of the Mossad) that rescued tens of thousands of European Jews from the Nazis by shipping them to Palestine in rickety boats. Many of these boats were intercepted and some sank with great loss of life. The efforts began in 1939, and the last immigrant boat to try to enter Palestine before the end of the war was MV "Struma", torpedoed in the Black Sea by a Soviet submarine in February 1942. The boat sank with the loss of nearly 800 lives.