During the Jewish insurgency in Palestine, he took part in anti-British operations. In April 1946, he participated in a major operation to sabotage the railway network in southern Palestine, and was severely wounded in the arm. While recuperating from his injury, which prevented him from using a gun, he worked in the Irgun's propaganda department, where he was director of its foreign press section. In 1947, he was transferred to Jerusalem, and served as a commander during the 1947-1948 Civil War in Mandatory Palestine. Initially, his role was to train new recruits. His most notable action during this period was taking part in a joint Irgun-Lehi attack on the Arab village of Deir Yassin, it what would later become known as the Deir Yassin massacre. After Benzion Cohen, the overall Irgun commander of the operation, was wounded, he took charge of the Irgun force and led it through most of the fighting.