The Third Phase (15 May - 19 July), considered the critical one, opened with the simultaneous, coordinated assault on the fledgling state by five regular Arab armies from neighboring countries, with an overwhelming superiority of heavy equipment - armor, artillery and airforce.
On 31 May the Haganah was renamed the "Israel Defence Forces". The IDF suffered initial setbacks, including the loss of the Etzion Bloc in Judea, the area of Mishmar Hayarden in the north and Yad Mordehai in the south, but after three weeks was able to halt the offensive, to stabilize the front and even initiate some local offensive operations.
The Fourth Phase (19 July 1948 - 20 July, 1949) was characterized by Israeli initiatives: Operation Yoav, in October, cleared the road to the Negev, culminating in the capture of Be'er Sheva; Operation Hiram, at the end of October, resulted in the capture of the Upper Galilee; Operation Horev in December 1948 and Operation Uvda in March 1949, completed the capture of the Negev, which had been alotted to the Jewish State by the United Nations.
Simultaneously, the Arab countries signed Armistice Agreements: first came Egypt - 24 February 1949; followed by Lebanon - 23 March; Jordan - 3 April; and Syria - 20 July. Only Iraq did not sign an armistice agreement with Israel. It preferred to withdraw its troops and hand over its sector to the Arab Legion of Jordan.
In the end Israel not only ejected the invading Arab forces - it also captured and held some 5,000 km2 over and above the areas allocated to it by the United Nations.
In the middle of the War of Independence, the IDF was born, not on 15 May, but two weeks later; for two more weeks Ben-Gurion negotiated with the "dissident" armed organizations, the Etzel and Lehi, convincing them to disband voluntarily before he disbanded them in the Order of the Establishment of the IDF on 31 May 1948. That order provided for only one armed force, subordinate to the constitutional government. There was complete continuity between the Haganah and the IDF: Ya'acov Dori, the Chief of Staff; the members of the General Staff; the commanders from brigade-level downwards - all were automatically confirmed in their appointments.
At the end of the war the IDF had over 100,000 full-time men and women in uniform, as compared to the mere handful of full-time soldiers at its beginning. In addition to 12 brigades, mostly infantry, it had several regiments of artillery. The first armored regiments were equipped with light armored vehicles, some captured, some "requisitioned" from the departing British troops; and a few tanks - two Cromwells "bought" from the withdrawing British and some reconstituted from American scrap.
The Navy consisted at first of reconverted illegal immigrant vessels. There were the elements of an Air Force - Spitfires and Messerschmidts, acquired mainly in Czechoslovakia, in addition to the light civilian planes which the Haganah had used for reconnaissance and communications purposes. Some World War II US war surplus bombers were bought as scrap. These carried out their first "strategic attack" on Cairo, en route to Israel, even before reaching their homebase. Armed with a Baedeker tourist guide, one of them bombed and strafed Abdeen Palace: rudimentary, to be sure, but entirely unexpected and, therefore, psychologically effective.
As soon as the armistice agreements were signed and the immediate danger had passed, the IDF - except for a small nucleus - was not only demobilized, but effectively disbanded. The new state had urgent tasks which required all its resources, above all that of absorbing the flood of new immigrants, who at last were able to come "home". An attempt to keep the demobilized soldiers in some sort of reserve framework failed. However, for the time being there was little inclination on the Arab side to renew full-scale fighting. Not that they had come to face reality and recognized Israel - far from it; but they did realize that to fight against Israel required thorough preparation.
In the meantime they found what was considered a perfect tool to show their own people that the war was not over yet and at the same time both to harrass Israel and embarrass her. Palestinian fedayun (suicide troops) infiltrated across the long and ill-protected border - and it should be recalled that no place in Israel was far from the border: infiltrations for the purpose of stealing farm equipment were followed by the laying of mines, the killing of individuals, and wholesale massacres. The fedayun were trained, equipped and paid for by Egyptian Intelligence, although they operated mainly from bases in Jordan, so that Jordan would bear the brunt of Israel's retaliation, which inevitably followed. And each time Israel retaliated, the Security Council condemned it; condemnation of an Arab government had long since become an impossibility, because of the Soviet veto.
The infiltrations - however painful, militarily and diplomatically - were no more than a diversion from the main concern of the IDF: preparations for the second round.
Yigael Yadin, who had taken over from Ya'akov Dori as Chief of the General Staff, devoted his energy to organizing the reserves and streamlining the command structure - elements of which remain in effect to this day. At the same time, particular attention was paid to the development of armor. Israel's numerical inferiority to its neighbors and potential enemies; its realization that because of the lack of strategic depth it was bound to transfer fighting as soon as possible to enemy territory and its proven advantage at swift, often improvised manoeuvers - all pointed to the need for armor. The newly found alliance with France at the time of the Suez crisis provided the unique opportunity to equip a major part of the IDF with French-made tanks. This "miracle" occurred at a moment of desperation, when no other country, East or West, was willing to supply Israel with arms, whereas countries from both East and West rushed to offer their wares to the Arabs. Particularly worrisome was the Czech-Egyptian arms deal, which threatened Israel with a whole range of state-of-the-art Russian hardware.