AUDIO: We interrupt our program to bring you a special broadcast. The German news agency Transocean said today in a broadcast that the Allied invasion had begun. EISENHOWER: A landing was made this morning on the coast of France by troops of the Allied Expeditionary Force. This landing is part of a concerted United Nations plan for the liberation of Europe. [:20]

         Dwight Eisenhower confirmed what Americans had been hearing for hours: It was D-Day for the war in Europe. Thousands of ships and aircraft, and about 160,000 troops, were invading the beaches of Normandy 75 years ago today.

         The Moon played a crucial role in the success of that invasion -- through its light, and through its influence on the tides.

         The invasion would begin around midnight, when paratroopers and gliders dropped behind the beaches. They’d need light to see what they were doing, so planners wanted a full or almost-full Moon.

         More important, they wanted the tides to be just right. German defenders had placed obstacles on the beaches to wreck landing craft coming in at high tide. So planners wanted a fairly low tide, allowing craft to land below the obstacles. But they didn’t want the tide to be too low, because then Allied troops would have to cross a wider section of beach against enemy fire.

         Using mechanical computers, an Allied team calculated that the best days for the invasion were June 5th, 6th, and 7th, 1944, when the Moon would be full and the tides would be just right at dawn. The weather looked bad for the 5th, so Eisenhower gave the go-ahead for June 6th: D-Day.

Script by Damond Benningfield