- Physical Review publishes 1st paper to deal with "black holes"
- Switzerland mobilizes its forces and the Swiss Parliament elects Henri Guisan to head the Swiss Army (an event that can happen only during war or mobilization).
- Switzerland proclaims neutrality
- The Wound Badge for Wehrmacht, SS, Kriegsmarine, and Luftwaffe soldiers is instituted. The final version of the Iron Cross was also instituted on this date.
- World War II starts as Germany invades Poland by attacking the Free City of Danzig
Day of the Week: Friday