D-Day simply means "the day of the operation," just as H-Hour means "the hour of the operation." It's a variable used in military planning when the actual date hasn't been set. Every military operation has a D-Day; June 6, 1944, just became the most famous one.

Source: U.S. Army Center of Military History

Russia and Germany did not formally end their state of war until 1955, when the Soviet Union issued a decree ending it. A final peace settlement for Germany was not reached until the Two Plus Four Agreement in 1990.

Source: Norman Naimark, The Russians in Germany

Switzerland was bombed over 70 times during the war by both sides. The most serious incident was the American bombing of Schaffhausen on April 1, 1944, which killed 40 people. The U.S. paid 62 million Swiss francs in reparations.

Source: Jonathan Steinberg, Why Switzerland?

Germany laid down the carrier Graf Zeppelin but never completed it. Italy converted two liners but they were never operational. Japan operated over 25 carriers during the war, more than any other navy.

Source: Mark Stille, Imperial Japanese Navy Aircraft Carriers

The V-2 used a 75% ethanol/25% water mixture as fuel, with liquid oxygen as the oxidizer. The ethanol was often diverted from potato schnapps production, leading to the dark joke that the V-2 program consumed more alcohol than the entire Wehrmacht.

Source: Michael Neufeld, The Rocket and the Reich