August 2: Albert Einstein writes to President Franklin Roosevelt about developing the atomic bomb using uranium. This leads to the creation of the Manhattan Project.
August 4: Neville Chamberlain dismisses Parliament until October 3.
August 15: MGM's classic musical film The Wizard of Oz, based on L. Frank Baum's famous novel, and starring Judy Garland as Dorothy, premieres at Grauman's Chinese Theatre in Hollywood.
August 19: Hitler, after evaluating the pace of the non-aggression negotiations with the Soviet Union, orders the Kriegsmarine to begin the opening operations for Fall Weiss, the invasion of Poland. The German pocket battleship Admiral Graf Spee, along with the German pocket battleship Deutschland, as well as dozens of u-boats, cast off for their advance positions. According to William L. Shirer, Hitler spends the next few days worrying that the Russians will not come to terms in time for the rest of the invasion plans to unfold as scheduled.
August 20: Armored forces under the command of Soviet General Georgi Zhukov deliver a decisive defeat to Japanese Imperial Army forces in the Japanese-Soviet border war in Inner Mongolia.
August 23: Molotov-Ribbentrop Pact signed between Germany and the Soviet Union, a neutrality treaty that also agreed to division of spheres of influence (Finland, Estonia, Latvia, eastern Poland and Bessarabia (today Moldova), north-east province of Romania to the Soviet Union; Lithuania and western Poland to Germany).
August 24: As details of the Molotov-Ribbentrop Pact become public, Neville Chamberlain recalls the Parliament of the United Kingdom several weeks early. In a burst of legislation, a War Powers Act is approved; and HMG order the Royal Navy to be put on a war footing, all leaves to be cancelled, and the Naval and coast defense reserves to be called up, especially radar and anti-aircraft units. In addition, the last British and French private citizens in Germany are ordered home by their respective Governments.
August 25: The German Foreign Ministry cuts off all telegraph and telephone communication with the outside world in accordance with the plan for Fall Weiss. At approximately 1830 Central European time, Adolf Hitler postpones Fall Weiss for 5 days, after receiving a message from Benito Mussolini that he will not honor the Pact of Steel if Germany attacks Poland, and because Chamberlain's government has not fallen as a result of the German-Soviet Non-Aggression Pact. Some units already in their forward positions (the attack is scheduled for 0430 the next day) do not get the word in time and attack various targets along the border. That same day, Neville Chamberlain gives Edward Rydz-S'mig?y his "ironclad guarantee" of assistance if Poland is attacked by Germany.
August 25: An Irish Republican Army bomb explodes in the centre of Coventry, England, killing 5 people. - MGM's classic musical film The Wizard of Oz, based on L. Frank Baum's famous novel, and starring Judy Garland as Dorothy, is released in theaters everywhere.
August 26: Division of Grazing renamed U.S. Grazing Service. - The Kriegsmarine orders all German-flagged merchant ships to head to German ports immediately in anticipation of the invasion of Poland.
August 27: A Heinkel 178, the first turbojet-powered aircraft, flies for the first time with Captain Erich Warsitz in command.
August 30: Poland begins a mobilization against Nazi Germany. (source: Wikipedia)