Chapter XIX of the United Nations Charter deals with ratification and signature of the UN Charter. It provided that the Charter would enter into force once ratified by the Permanent Five members of the United Nations Security Council and a majority of the other signatory states. The Charter was opened for signature on 26 June 1945 and entered into force on 24 October 1945, which became known[by whom?] as United Nations Day. In the meantime, the atomic bombings of Hiroshima and Nagasaki took place on August 6 and 9, respectively; the introduction of this new weapon of warfare completely changed the security environment in which the UN Charter was promulgated.