21 September 1940 
War in the Air
Luftwaffe attacks London and towns in the south east
RAF attacks invasion bases 
North Africa
Sidi Barrani is bombed    
How to cite this article: Rickard, J (28 December 2007), 21 September 1940 , https://www.historyofwar.org/secondworldwar/date/1940_09_21.html