D-Day Summary
A lot of planning went into the Allied invasion of France on June 6, 1944. The plan was made up of a few overlapping plans each given codenames to refer to specific, important operations. The codename for the invasion of northwest Europe was known as Operation Overlord. The assault phase (D-Day) was codename Operation Neptune. Operation Neptune required the Allied forces to establish a foothold in Normandy.
One key component of Neptune to be considered was the weather. Only 10 days each month were considered suitable to launch the operation. A full moon was needed for the illumination of key landmarks for landing craft and support aircraft. The Allied forces also needed to be able to see the obstacles and barriers placed by the Germans in the surf and on the beaches of the landing sites. Also, the full moon meant a high tide for the ships and landing craft to be able to get in close to the beaches safely.
Since a full moon was scheduled for June 6, the planned date of the attack was set at June 5th. However, the weather was bad on June 4th and it looked like everything might have to be canceled. If canceled, the next window of attack would not be available for a full month. General Eisenhowers staff meteorologist made a last second forecast that indicated the weather would improve just enough to be able to carry out Operation Neptune.
Although the weather limited air support for the Allies, the Germans believed no invasion was possible because of the severity of the weather. Many of the German troops were standing down and many officers were away for the weekend when the attack occurred. The weather turned out to be just good enough, or bad enough to help the Allies in their successful invasion of Normandy.