After the U.N. resolution about the partition of Palestine and establishment of a Jewish state, Hagana was the only fighting force, which defended the Jewish population against the mounting Arab attacks.
During this stage of the war the Hagana started to transform itself into a regular army in order to defend the Yishuv and later the new State against the imminent invasion of the surrounding Arab armies.
The Jewish nation is indebted to the Hagana for its achievements, from the early days of the Yishuv: its constant growth and strengthening as a national military organization between the two World Wars; the formation of the Settlement Police Force, the Palmach, Hish , Chim (Home Guard); sending its members to join the British forces, especially the Jewish Brigade during the second world war; and finally defending the Yishuv in the fierce battles against the assaulting Arabs, from November 1947 to May 1948, when it became the IDF.
David Ben Gurion, the first Prime Minister and the Minister of Defense of Israel, proclaimed in the first IDF Order of the Day, in May 1948: "The Yishuv would have never survived these 6 months of bloodshed, and the State of Israel would not survive were it not for the Hagana's experience, command skills, loyalty and courage".

Nearly six thousand members of the Hagana were killed in action during the War of Independence.

Hagana brigades which became IDF brigades:
Brigade No. 1- Golani - Battalions 11, 12, 13, 14, 15

Brigade No. 2 - Carmeli - Battalions 21, 22, 23

Brigade No. 3 - Alexanderoni - Battalions 31, 32, 33, 34, 35

Brigade No. 4 - Kiryati - Battalions 42, 43, 44

Brigade No. 5 - Givati - Battalions 51, 52, 53, 54, 55

Brigade No. 6 - Etzyoni - Battalions 61, 62, 63

Brigade No. 7 - Battalions 71, 72, 73/79

Brigade No. 8 - Battalions 82, 88, 89

Brigade No. 9 - Oded - Battalions 91, 92

Brigade No. 10 - Palmach-Harel - Battalions 4, 5, 6, 10

Brigade No. 11 - Palmach-Yiftach - Battalions 1, 2, 3

Brigade No. 12 - Palmach-Hanegev - Battalions 7, 8, 9