A Zionist military strategy, created by the Haganah and operationalized in April and May 1948 with several precursors in the previous decade (Plans Aleph, Bet, and Gimmel, the latter also known as the “May Plan”). Plan Dalet (or Plan D) was designed to secure control of the areas allocated to the Jewish state under the United Nations Partition Plan (1947) as well as areas outside it that were occupied by Jews (such as Jerusalem, which at the time was designated by the UN as having a special international status that would not be part of either the Jewish or the Arab state). Plan Dalet laid out 13 military operations which, had they all succeeded, would have left the entire country under Zionist control, including Jerusalem and areas allocated to the Arab state by the UN partition plan. In the end, not all of the operations were successful and the country, including Jerusalem, was subsequently divided.
See The West Side Story.