Haganah militants received clandestine military support from Poland and sought cooperation with the United Kingdom in the event of an Axis-led invasion of Palestine through North Africa, prompting the creation of the Palmach, their elite fighting force, in 1941.

Following the end of World War II, the British refused to lift the restrictions on Jewish immigration that they had imposed with the 1939 White Paper.

Shortly after the beginning of the 1948 Arab–Israeli War, Haganah was merged with other paramilitary groups and reorganized into the official military force of the State of Israel.

After the Arab riots against Jews in April 1920, the Yishuv's leadership saw the need to create a nationwide underground defense organization, and the Haganah was founded in June of the same year.

During the 1947–48 civil war between the Arab and Jewish communities in what was still Mandatory Palestine, a reorganized Haganah managed to defend or wrestle most of the territory it was ordered to hold or capture.

At the beginning of the ensuing 1948–49 full-scale conventional war against regular Arab armies, the Haganah was reorganized to become the core of the new Israel Defense Forces.

Haganah "units" were very localized and poorly armed: they consisted mainly of Jewish farmers who took turns guarding their farms or their kibbutzim.

It also acquired foreign arms and began to develop workshops to create grenades and simple military equipment, transforming from an untrained militia to a capable underground army.

[citation needed] During the 1936–1939 Arab revolt in Palestine, the Haganah worked to protect British interests and to quell the rebellion using the Posh and then the Hish units.

[10] By 1939, the British had issued the White Paper, which severely restricted Jewish immigration to Palestine, deeply angering the Zionist leadership.

[citation needed] In 1940 the Haganah sabotaged the Patria, an ocean liner being used by the British to deport 1,800 Jews to Mauritius, with a bomb intended to cripple the ship.

[12][13] In the first years of World War II, the British authorities asked Haganah for cooperation again, due to the fear of an Axis breakthrough in North Africa.

[citation needed] In 1943, after a long series of requests and negotiations, the British Army announced the creation of the Jewish Brigade Group.

[14] On May 14, 1941, the Haganah created the Palmach (an acronym for Plugot Mahatz – strike companies), an elite commando section, in preparation against the possibility of a British withdrawal and Axis invasion of Palestine.

[17] It was never large – by 1947 it amounted to merely five battalions (about 2,000 men) – but its members had not only received physical and military training, but also acquired leadership skills that would subsequently enable them to take up command positions in Israel's army.

[citation needed] Future Jerusalem mayor Teddy Kollek was later revealed to be a Jewish Agency liaison officer working with the British authorities who had passed on information that led to the arrest of many Irgun activists.

[19] The Irgun, paralyzed by the Saison, were ordered by their commander, Menachem Begin, not to retaliate in an effort to avoid a full blown civil war.

The Saison eventually ended due to perceived British betrayal of the Yishuv becoming more obvious to the public and increased opposition from Haganah members.

[22] The Palmach performed a single assassination operation in which a British official who had been judged to be excessively cruel to Jewish prisoners was shot dead.

[24] In addition to its operations, the Haganah continued to secretly prepare for a war with the Arabs once the British left by building up its arms and munitions stocks.

It maintained a secret arms industry, with the most significant facility being an underground bullet factory underneath Ayalon, a kibbutz that had been established specifically to cover it up.

As Palmach members refused to participate, a unit of about 200 men from regular Haganah units was mobilized, and foiled several operations against the British, including a potentially devastating attack on the British military headquarters at Citrus House in Tel Aviv, in which a Haganah member was killed by an Irgun bomb.

[19][29] After "having gotten the Jews of Palestine and of elsewhere to do everything that they could, personally and financially, to help Yishuv," Ben-Gurion's second greatest achievement was his having successfully transformed Haganah from being a clandestine paramilitary organization into a true army.

Famous members of the Haganah included Yitzhak Rabin, Ariel Sharon, Rehavam Ze'evi, Dov Hoz, Moshe Dayan, Yigal Allon and Dr. Ruth Westheimer.

Sheik Hussein Mohammed Ali Abu Yussef of Tuba was quoted in 1948 as saying, "Is it not written in the Koran that the ties of neighbors are as dear as those of relations?