An acronym for Lohamei Herut Yisrael (Fighters for the Freedom of Israel), Lehi was an underground organization that operated from 1940 to 1948. At first, it was composed chiefly of a group headed by Avraham ("Yair") Stern, that broke off from Etzel in 1940. The split was due to disagreement on three main issues: (a) the group's demand that the military struggle against the British government be continued irrespective of the war against Nazi Germany; (b) opposition to enlistment in the British army, which Jabotinsky supported; and (c) willingness to collaborate, as a tactical measure, with anyone who supported the struggle against the British in Palestine.
Lehi's goals were maximalist: conquest and liberation of Eretz Israel; war against the British Empire; complete withdrawal of Britain from Palestine; and establishment of a "Hebrew kingdom from the Euphrates to the Nile." In contrast to the scope of these goals, Lehi's strength was limited; it never had more than a few hundred fighters and its arms stores were meager. The disparity between its aspirations and its real power dictated Lehi's method of fighting: bold, extremist actions, intended both to obtain funding and weapons and to demonstrate that it was possible to strike at the enemy successfully.
As a result of its activities, Lehi found itself isolated in the yishuv. The yishuv's institutions condemned it and the British police hunted its members. On February 12, 1942, Avraham ("Yair") Stern, the leader of Lehi, was captured in a Tel Aviv apartment and murdered by British detectives. The remaining fighters continued to wage his war, and a new command structure was established. Terrorism continued to be the organization's guideline, in the belief that a series of painful attacks would force the British to re-evaluate the wisdom and price of remaining in Palestine.
On November 6, 1944, two Lehi members assassinated Lord Moyne, the British Minister for Middle East Affairs in Cairo. The perpetrators, Eliyahu Beit-Tzuri and Eliyahu Hakim, were caught, tried by a military tribunal, and hanged on March 23, 1945.
When the Hebrew Resistance Movement was founded in November 1945, Lehi joined it, along with the Haganah and Etzel. Lehi carried out several operations as part of the movement, the largest of which was the bombing of the Haifa railroad workshops in June 1946, in which 11 Lehi members were killed. After the Hebrew Resistance Movement broke up following Etzel's bombing of the King David Hotel in Jerusalem on July 22, 1946, Lehi continued with its harassment and attrition policy.
When the IDF was established on May 31, 1948, Lehi was disbanded and its members enlisted in the IDF. Only in Jerusalem did Lehi remain an independent organization, arguing that at the time of the proclamation of independence the city's fate had not yet been determined. On September 17, 1948, Swedish Count Folke Bernadotte, a UN mediator, was assassinated in Jerusalem, and Lehi members were suspected. The government outlawed the organization's branch in Jerusalem and shut down its publication, Hamivrak. The leaders of Lehi, Natan Yellin-Mor and Mattityahu Shmuelevitz, were sentenced to long jail terms by a military court, but were released in a general amnesty.
Sources: Israeli Foreign Ministry