Khalidi, Walid. 'Plan Dalet: Master Plan for the Conquest of Palestine'; Pappe, Ilan.
Ben-Gurion invested Yigal Yadin with the responsibility to come up with a plan in preparation for the announced intervention of the Arab states. The result of his analysis was Plan Dalet, which was put in place from the start of April onwards. The adoption of Plan Dalet marked the second stage of the war, in which Haganah passed from the defensive to the offensive.
Dominique Lapierre et Larry Collins , pp.369-381 The success of the operation was assisted by the death of Al-Hassayni in combat. During this time, and independently of Haganah or the framework of Plan Dalet, irregular troops from Irgun and Lehi formations massacred a substantial number of Arabs at Deir Yassin, an event which, though publicly deplored and criticized by the principal Jewish authorities, had a deep impact on the morale of the Palestinian population.
Source: Wikipedia > Plan Dalet
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