The Cement Incident took place in the port of Jaffa in Palestine on 16 October 1935. While Arab dockers were unloading a consignment of 537 drums of White-Star cement from the Belgiancargo shipLeopold II, which were destined for a Jewish merchant called J. Katan in Tel Aviv, one drum accidentally broke open spilling out guns and ammunition. Further investigation by British Mandate officials revealed a large cache of smuggled weapons, comprising 25 machine guns, 800 rifles and 400,000 rounds of ammunition contained in 359 of the 537 drums, but because the merchant was not identified and the final destination was not uncovered no arrests were made. Almost overnight, protests erupted throughout Palestine and swept other major Arab urban cities, including Amman, Cairo, Damascus, and Baghdad. Alongside other groups in Palestine, Al-Qassam carried out incursions against British Mandate forces and Jewish settlers.
General alarm in the Arab press over the arms discovery and the failure of the British authorities to take action was followed by a general strike on 26 October, which was widely observed and became violent in Jaffa. At the end of October, in response to the storm of public controversy over the arms shipment, Sheikh Izz ad-Din al-Qassam, a reformist preacher, leader of the Black Hand, an anti-Zionist and anti-British militant organisation, approached his followers with a proposal to take up arms. He recruited and arranged military training for peasants and by 1935 he had enlisted between 200 and 800 men. The cells were equipped with bombs and firearms, which they used to kill Jewish residents in the area, as well as engaging in a campaign of vandalism of settler-planted trees and British-constructed rail-lines. In November 1935, two of Qassam's men engaged in a firefight with a Palestine police patrol hunting fruit thieves and a policeman was killed. Following the incident, British police launched a manhunt and surrounded al-Qassam in a cave near Ya'bad. In the ensuing battle, al-Qassam was killed. Qassam's funeral in Haifa became a major nationalist demonstration attended by thousands and Qassam was subsequently regarded as a nationalist cult hero and became an inspiration to diverse Palestinian nationalist groups, not least during the ensuing Great Revolt of 1936-1939, which his death helped to spark six months later.