The Largest Amphibious Force In History Assembled To Break Hitler's Supposedly Invincible Line Of Defence. Early in the morning of 6th June 1944, a vast and bizarre armada ploughed steadily against stiff head-winds through the rough waters of the English Channel, heading for the Normandy coast. Amongst the 5,000 vessels were many of the best British and American warships of stupendous collective firepower, also ancient battleships and tankers on their last voyage, destined to be sunk to provide breakwaters. It was D-Day. Conceived almost on the shores of Dunkirk, four years in the planning, two in the organising and one day in execution, the landing in Normandy was easily the largest and most extraordinary combined military operation ever attempted. It was also a crucial one.