WHAT ALL HAPPENED MAY TO SEPTEMBER 1939
Find out what all happened May to September 1939

Albert Einstein and Leó Szilárd write a letter to Franklin D. Roosevelt, urging him to begin the Manhattan Project to develop a nuclear weapon. (2. August 1939)

Siam is renamed Thailand by Plaek Pibulsonggram, the country's third prime minister. (24. June 1939)

World War II: A German U-boat U 29 sinks the British aircraft carrier HMS Courageous. (17. September 1939)

World War II: The Battle of Kępa Oksywska concludes, with Polish losses reaching roughly 14% of all the forces engaged. (19. September 1939)

World War II: The United Kingdom and France begin a naval blockade of Germany that lasts until the end of the war. This also marks the beginning of the Battle of the Atlantic. (3. September 1939)

General Władysław Sikorski becomes commander-in-chief of the Polish Government in exile. (30. September 1939)

Nazi Germany mounts a staged attack on the Gleiwitz radio station, creating an excuse to attack Poland the following day thus starting World War II in Europe. (31. August 1939)

World War II: Canada declares war on Germany, the country's first independent declaration of war (11. September 1939)

First flight of the German Focke-Wulf Fw 190 fighter-bomber airplane. (1. June 1939)

The Canadian National War Memorial is unveiled by King George VI and Queen Elizabeth in Ottawa. (21. May 1939)

The United Kingdom and Poland form a military alliance in which the UK promises to defend Poland in case of invasion by a foreign power. (25. August 1939)

World War II: Germany and Italy sign the Pact of Steel. (22. May 1939)

The Nazi propaganda broadcaster known as Lord Haw-Haw begins transmitting. (18. September 1939)

Holocaust: the last remaining Jewish enterprises in Germany are closed. (6. July 1939)

The Baseball Hall of Fame opens in Cooperstown, New York. (12. June 1939)

World War II: The Battle of Hel begins, the longest-defended pocket of Polish Army resistance during the German invasion of Poland. (9. September 1939)

World War II: The Battle of Barking Creek. (6. September 1939)

Warsaw surrenders to Nazi Germany during World War II. (28. September 1939)

World War II: Polish government of Ignacy Mościcki flees to Romania. (18. September 1939)

Adolf Hitler signs an order to begin the systematic euthanasia of mentally ill and disabled people. (1. September 1939)