Illegal immigration had begun before World War II, and a few ships attempted to bring Jews to Palestine during the war. One attempt ended tragically in Istanbul Harbor when the Struma, a ship carrying 800 Jewish refugees from Romania, was sunk by a Soviet submarine, resulting in the deaths of almost all its passengers.

Once the war ended, survivors in Europe, primarily those in Eastern Europe, began moving westward, crossing over to Allied lines. Most of the refugees were placed in Displaced Persons Camps, but many did their best to make their way to Palestine. The Yishuv organized a campaign of illegal immigration called Aliyah Bet. Old ships were purchased or chartered to make their way to Palestine in the hope of avoiding the British blockade. Most were stopped, and their passengers were sent to detention camps first in Atlit and then to Cyprus, but a few succeeded in sneaking past the blockade and landing their passengers in Palestine.

The most famous ship was the Exodus. It had been named President Warfield and had plied the waters of Chesapeake Bay before the war. During the war, it had been turned over to the British Royal Navy and was returned to the US at the end of the war. The Haganah purchased it in the US to use for running the blockade. It was hoped that the ship would be able to beach itself on the shore. The boat traveled to Sete, France, where 4,000 Jews boarded the ship. On July 11th, the ship left the port, ostensibly bound for Istanbul. The British closely followed the ship. On July 18th, with the ship about 20 miles off the coast, the British tried to board the vessel, but the Haganah refugees and members aboard resisted. The battle was broadcast live on the ship's radio and relayed throughout Palestine. Finally, the British turned their machine guns on the boat, killing two passengers with gunfire; they also clubbed to death the second officer, an American Machal volunteer named Bill Bernstein.

The ship was then towed into Haifa Harbor. The British decided to force the refugees to return to France, so they offloaded the passengers and forced them onto three other ships. This was done as representatives of the United Nations Commission on Palestine were observing. The ships returned to France, but the French said they would only accept the refugees back if the refugees would disembark willingly. They were unwilling, and the British decided they had no choice but to transport the 4,500 Holocaust survivors to the British Zone of occupation in Germany. The Exodus story received worldwide publicity and is said to have affected some of the members of UNSCOP. The story of Exodus became a best-selling book and a major motion picture.