April: Scientists Ralph Alpher and George Gamow publish the Alpher-Bethe-Gamow paper about the big bang.

April 3: President Harry Truman signs the Marshall Plan, which authorizes $5 billion in aid for 16 countries. - Ludwig van Beethoven's Ninth Symphony is played on television in its entirety for the first time, in a concert featuring Arturo Toscanini conducting the NBC Symphony Orchestra. The chorus is conducted by Robert Shaw. - Jeju Uprising, Jeju residents revolt on Jeju island, South Korea.

April 5: 1947-1948 Civil War in Mandatory Palestine: Haganah launches Operation Nahshon; beginning of the 1948 Palestinian exodus.

April 7: The World Health Organization is established by the United Nations. - A fire in a Buddhist monastery Shanghai kills 20 monks.

April 9: Jorge Eliecer Gaitan's assassination provokes a violent riot in Bogota (the Bogotazo), and a further 10 years of violence in all of Colombia (La Violencia). - The Deir Yassin massacre takes place in British Mandate of Palestine.

April 13: The Hadassah medical convoy massacre takes place in British Mandate of Palestine.

April 16: The Organisation for Economic Co-operation and Development is founded as the OEEC.

April 18: The first democratic general election with universal suffrage is held in Italy.

April 19: Burma joins the United Nations.

April 24: The Costa Rican Civil War ends.

April 30: Organization of American States (OAS) founded.

April 30: The Land Rover is unveiled at the Amsterdam Motor Show. (source: Wikipedia)