Against the background of a possible German invasion of Palestine on May 16, 1941, the Palmach was created to establish an elite ready reserve for the Haganah. The Palmach consisted of full time soldiers, who worked 14 days per month on kibbutzim, and trained for another 10 days. Between 1941 and 1943, there was close cooperation between the Palmach and the British, with the British using Palmach units for behind-the-lines assaults in Vichy-dominated Lebanon and Syria. By 1943, as the Axis threat receded, the British began to fear the Palmach might become a threat to their continued rule in Palestine. Therefore, they began to make unsuccessful attempts to suppress the Palmach. From late 1945 to mid-1946, the Palmach worked together with the Irgun, in attempts to undermine British rule in Palestine. From 1946 until 1947, the Palmach concentrated on helping facilitate Jewish immigration to Palestine. When the War of Independence began, the Palmach was the only ready standing army available to repel the Arab attack. The Palmach fought valiantly during the war, but sustained heavy casualties. In the midst of the war, Ben-Gurion dissolved the independent structure of the Palmach, and merged it into the IDF.