Short answers, pulled from the story.
Operation Bodyguard aimed to convince Adolf Hitler that the main Allied attack would strike at Pas-de-Calais instead of the actual target in Normandy. Planners created a fictitious First United States Army Group under Lieutenant General George S. Patton stationed in Kent and Sussex to deceive German listeners.
Eisenhower chose the 6th of June 1944 because weather conditions predicted by Group Captain James Stagg would improve enough for the operation to proceed. Postponing beyond this date meant waiting two weeks until the 18th to the 20th of June which risked exposing the plan to German intelligence.
Over 13,000 men from the 82nd and 101st Airborne Divisions were delivered by Douglas C-47 Skytrains during the initial assault. Paratroops from the 101st Airborne began dropping around 01:30 while units of the 82nd Airborne arrived by 02:30 to capture objectives like bridges over the River Merderet.
Casualties reached around 2,000 as men faced fire from cliffs above while wading through water up to their necks. DD tanks of two companies flooded and sank before reaching shore contributing to the heavy resistance from the 352nd Infantry Division.
Admiral Sir Bertram Ramsay commanded an invasion fleet drawn from eight different navies comprising 6,939 vessels. The majority came from the UK which provided 892 warships and 3,261 landing craft with total naval personnel numbering 195,700.