September: The U.S. Army 45th Infantry Division (previously a National Guard Division in Arizona, Colorado, New Mexico, and Oklahoma), is activated and ordered into federal service for 1 year, to engage in a training program in Ft. Sill and Louisiana, prior to serving in WWII.

September 2: An agreement between America and Great Britain is announced to the effect that 50 U.S. destroyers needed for escort work will be transferred to Great Britain. In return, America gains 99-year leases on British bases in the North Atlantic, West Indies and Bermuda.

September 5: Commerce raiding German auxiliary cruiser Komet enters the Pacific Ocean via the Bering Strait after crossing the Arctic Ocean from the North Sea with the help of Soviet icebreakers Lenin, Stalin, and Kaganovich.

September 7: Treaty of Craiova: Romania loses Southern Dobrudja to Bulgaria. - The Blitz - Nazi Germany begins to rain bombs on London (the first of 57 consecutive nights of strategic bombing).

September 12: In Lascaux, France, 17,000-year-old cave paintings are discovered by a group of young Frenchmen hiking through Southern France. The paintings depict animals and date to the Stone Age. - The Hercules Munitions Plant in Succasunna-Kenvil, New Jersey explodes, killing 55 people.

September 16: The Selective Training and Service Act of 1940 is signed into law by Franklin D. Roosevelt, creating the first peacetime draft in U.S. history.

September 17-September 18: SS City of Benares is torpedoed by German submarine U-48 in the Atlantic with the loss of 248 of the 406 on board, including child evacuees bound for Canada. This results in cancellation of the British Children's Overseas Reception Board's plan to relocate children overseas.

September 26: The United States imposes a total embargo on all scrap metal shipments to Japan.

September 27: Germany, Italy and Japan sign the Tripartite Pact. (source: Wikipedia)