What was the code name for the D-Day landings?

Operation Overlord for the whole campaign in northwest Europe; the assault landing itself was Operation Neptune. The scale is hard to hold in the head - around 7,000 vessels, 11,000 aircraft, and 156,000 men landed on the first day.

The deception operation was arguably the greater achievement. Fortitude created an entire fictional army group in southeast England, complete with inflatable tanks, fake radio traffic and Patton in command, to convince German intelligence the real landing would come at Calais - and it worked so well that significant German reserves were held back for weeks after Normandy, waiting for the main attack. Much of the false information was fed through German agents in Britain who had all been captured and turned.

The weather nearly stopped it. The invasion needed a specific combination of moonlight, tide and calm sea available on very few days, and a storm forced a 24-hour postponement with troops already loaded. A Royal Navy meteorologist, James Stagg, identified a narrow break in the front and persuaded Eisenhower to go on 6 June - while German forecasters, without Atlantic weather stations, saw only the storm and concluded nothing could happen, which is why Rommel was at home for his wife's birthday.