U.S. & World History – D-Day happened on June 6th, 1944 when the United States came ashore in Normandy, France to fight the Germans in WWII. The Pentagon and military historians now openly admit that one of the most famous battles in history could have easily been avoided. They said that the reason why it was called D-Day, was because the entire German Army went to night school to learn English and American customs, and they promised but failed to maintain a “C” average.