Operation Overlord was the 1944 campaign for the invasion of continental Europe in World War II. It was fought by the Allied forces against German forces. The most critical part was the Normandy landings, which were to get the Allied armies onto the continent of Europe. This might have failed. Heavy casualties were expected, even if it succeeded. It was successful. The Battle of Normandy raged until German forces retreated across the Seine on 30 August 1944. This marked the close of Operation Overlord.