The allies had been preparing for this day for a long time. So on the morning of June 6, 1944 thousands of allied troops landed on Normandy's beaches. Hundreds of our American men were killed as they stepped off the boats and were slaughtered by German soldiers with machine guns and artillery. Movies like Saving Private Ryan portray this bloody scene with an R rating (I have never seen the movie myself, but that is what I heard). Fierce fighting soon took place at places like St. Lo.
D-day was one of the bloodiest battles in they war.
If you have a question just leave a comment and I'll answer personaly.