Fifty-two countries signed the Chicago Convention on International Civil Aviation, also known as the Chicago Convention, in Chicago, Illinois, on 7 December 1944. Under its terms, a Provisional International Civil Aviation Organization was to be established, to be replaced in turn by a permanent organization when twenty-six countries ratified the convention. Accordingly, PICAO began operating on 6 June 1945, replacing ICAN. The twenty-sixth country ratified the convention on 5 March 1947 and, consequently, PICAO was disestablished on 4 April 1947 and replaced by ICAO, which began operations the same day. In October 1947, ICAO became an agency of the United Nations under its Economic and Social Council (ECOSOC).