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TIL while the word D-Day is most commonly used for the Normandy Landings in WW2, the term refers to any day on which a combat attack or operation begins. There have been many D-Days before and after WW2

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GEdg TIL 80% of the SR-71 Blackbird’s thrust at Mach 3.2 was generated from its ability to harness energy from the shock waves it created, thanks to special retractable spikes in front of its inlets. Its engines generated the other 20% of thrust.
b6Oap TIL it is dangerous to blow air into a pregnant women's vagina. The increased air pressure can pass beneath the fetal membranes and into the circulation causing a venous air embolism that can kill within minutes.
59Np TIL the platypus used to be considered a myth like Bigfoot and the Yeti
l70va TIL that lightsabers came from the pulp magazines! George Lucas cribbed the concept of "laser swords" from stories in 1930s pulps such as "Magic Carpet," "Weird Tales," and "Amazing Stories."
0AXM TIL a German mathematician spent a decade writing a 200 page manuscript about drawing a regular 65537 sided polygon with a compass and a straightedge