As Independence became a real option Ben-Gurion was clear about what needed to be done. In December 1946, after taking over the defense portfolio of the Jewish Agency, Ben-Gurion stated, "We now face a completely different situation. Palestine is surrounded by independent Arab countries. They can buy and produce weapons, establish armies, and train them. An attack by the Arabs of Palestine does not endanger the Yishuv. But there is a danger that the neighboring Arab states will send their armies to attack the Yishuv and destroy it. We must prepare immediately. This is the primary goal of Zionism.”
Even before giving the speech, Ben-Gurion was well aware of the challenges that lay ahead. In 1945, he recruited eighteen Jewish millionaires to form the Sonneborn Institute. Their job was to provide the money and secure military equipment, as well as machine tools to produce arms in Palestine. The group managed to secure a significant amount of arms manufacturing equipment in the US, which, after World War II, had a great deal available. They also managed to purchase four B-17s, some C-46s, and aviation fuel.
Haganah agents also scoured Europe for arms and were able to purchase 65mm artillery pieces, mortars, anti-aircraft guns, and some light tanks, as well as small arms. Many of the arms were smuggled in before the British pulled out. Once the mandate ended, they could bring in the arms legally.
Arms were only one part of the needs of the Yishuv to defend itself; the other part was troops. In early 1947, the Haganah had 35,000 troops, but only the 2,000 full-time Palmach members. In the fall of 1947, the Haganah began an effort to mobilize the population. By the end of December, the number of men under arms full-time had grown to 7,500, and by the time of Independence, that number had grown to 30,000. Once the war began, that number grew rapidly to 64,000.
At the same time, the Haganah reorganized itself into military units made up of brigades and battalions. By July, all the Haganah, Palmach, as well as the Etzel and Lechi units, had been organized into the IDF.