The idea of smuggling Jews into Palestine was already around already in the early 1930s, mainly attempts by small groups to cross the northern border from Syria and Lebanon. In July 1934, Haganah tried to smuggle Jews into the land by sea. To do so, they bought an old ship into which they could crowd 350 immigrants. On July 31, 1934, the ship completed the voyage from Piraeus to the Palestine shore and for four nights, small groups were transported from ship to the beaches of Kfar Vitkin and Tel Aviv. The Haganah tried to make another run with the ship, but at that stage, the British were on to them and managed to prevent the ship from reaching the shore.
When the 1939 white paper which almost completely ended legal immigration was published, clandestine immigration grew dramatically. In the eight months after the publication of the white paper, even after World War II began, 23 ships arrived carrying more than 14,000 clandestine immigrants. Some of them managed to evade the British blockade of the coast, while others were stopped and their passengers put in detention camps.
In November 1940, the British caught three large ships: the Pacific, Milos, and Atlantic. The British decided to change their policy and not send the passengers to a detention camp in Palestine where they were usually later released, but to deport them to the island of Mauritius. The immigrants were all transferred to a passenger ship called the Patria with the intent to deport them. The Patria was a French passenger ship, built in 1913, that had sailed the Haifa=Marseille route. When France surrendered to Germany the ship, in Haifa at the time, was confiscated by the British. They now planned to use her to deport the clandestine Jewish immigrants. To stop the deportation the Haganah decided to blow a hole in the ship. However, the attack was not planned well – the explosion from the underwater bomb attached to the ship’s hull caused it to sink within minutes. Over 200 immigrants died in the accident. The survivors were transferred to the detention camp at Atlit. Despite this tragedy, the British went ahead with the Mauritius plan, deporting 1,645 clandestine immigrants to the island and confining them to a camp there for five years. In 1945, the British permitted them to return to Palestine.
In late 1941, the Struma, a small ship that was barely seaworthy, set sail from Romania. When it reached Istanbul, the British demanded that theTurkish authorities stop the ship. After some deliberation, the Turks decided to tow it back out to the Black Sea. On February 24, 1942, in especially stormy waters, a huge explosion struck the ship and it sank quickly. All of its passengers except for one went down with it.
The emissaries of Aliyah Bet even ventured to Iraq, Syria, and Lebanon in a bid to bring clandestine immigrants through those countries.
The years between World War II and the establishment of the State of Israel were the peak of clandestine immigration; 85,000 clandestine immigrants arrived during this period. In 1946, the Mossad started to acquire larger ships, which the British discovered easily with a new line of radar stations built along the shore to locate and stop Haganah ships. The immigrants were transferred to the detention camp at Atlit.