May 9, 1940 -
Adolf Hitler issued the order to commence the invasion of France and the Low Countries at dawn on the following day. At noon German meteorologists made a firm forecast of clear skies on the following morning; Adolf Hitler gave the meteorology officer a medal on the spot. In the afternoon, Hitler departed Berlin, Germany for this temporary forward headquarters codenamed Felsennest near Bad Münsereifel in the Rhineland region of Germany to observe the coming invasion.
May 9, 1942 -
Joseph Rochefort's cryptanalytic team in Pearl Harbor, US Territory of Hawaii intercepted a Japanese Navy radio message ordering carrier Akagi to make rendezvous with another fleet at Sasebo, Japan on 20 May 1942. One of the US's first hint of the impending Jap strike on Target AF (later determined to be Midway Island)
May 9, 1944 -
Rudolf Höss returned to Auschwitz Concentration Camp and ordered the expansion of the rail platforms, the activation of Crematorium V, the reactivation of Bunker 2 (gas chamber), the digging of five pits, among other items, in preparation for the arrival of Hungarian Jews at Auschwitz