Popular Mechanics magazine has been around a lot longer than most people realize, and they sometimes cover topics that one wouldn't expect to find in a magazine by that name. One such topic covers in detail the planning behind the Normandy Invasion, which occurred 75 years ago today. The scope and depth of the planning is breathtaking, and it makes for spine-tingling reading even today, so much more impressive as it was planned without the use of computers.
I've read elsewhere about the many nuances of the planning, but, most surprisingly, it was the meteorologists that called the shots for exactly when this invasion would take place. They gave Eisenhower a narrow window during which the weather was predicted to be cooperative and he took it. The rest, as they say, is history.
Read through the article and, like me, gain newfound respect for the Greatest Generation.