The main countries involved in D-Day on the side of the Allies were the United States, the United Kingdom and Canada. There were also troops from Australia, Belgium, Czechoslovakia, France, Greece, the Netherlands, New Zealand, Norway and Poland. The only country in the Axis Powers to participate in the battle was Germany.
D-Day was originally scheduled for June 5, 1944, but poor weather conditions delayed it until June 6. The operations related to D-Day were Operation Overlord and Operation Neptune. Both operations began on D-Day. Operation Overlord referred to the Allied invasion of northwest Europe, and Operation Neptune was the assault phase that focused on establishing a beachhead in France. Operation Neptune was completed on June 30, 1944. Operation Overlord was completed on Aug. 19, 1944, after the Allies crossed the River Seine.
Approximately 156,000 Allied troops landed on D-Day. Troops came in by air and by sea. On the morning of D-Day, the Allies attacked five beaches in Normandy. The Allies continued to bring in troops and supplies, and by June 30, 1944 over 850,000 troops and 570,000 tons of supplies had landed. The invasion of Normandy was more successful than Allied Intelligence expected, and it was one of the largest German defeats of World War II.