On Tuesday, June 6, 1944, the Allied invasion of the Nazi-controlled European mainland began. Code-named “Operation Overlord,” it is still recognized as the largest military operation ever undertaken by air, land and sea — U.S., British and Canadian military numbered over 156,000.

Under the direction of the Supreme Allied Commander, U.S. Gen. Dwight D. Eisenhower, the troops descended on Normandy, the northern region of France that sits 100 miles across the English Channel from England.

Stormy weather delayed the invasion for 24 hours. But it had to proceed as moon phases and tides played a significant role in the operation. Aerial and naval bombing and airborne troop landings behind the German lines preceded the infantry invasion of the five beaches at Normady — Utah, Omaha, Gold, Juno and Sword. German Field Marshal Erwin Rommel had developed heavy fortifications along the northern coast of France in anticipation of an invasion, though he did not know exactly when or where it would occur.

Allied land forces, under the command of British Gen. Bernard Montgomery, endured heavy losses to take the beachheads, dodging mines, wooden stakes, barbed wire and other obstacles. More than 4,000 Allied troops, half of them American soldiers, lost their lives in the D-Day invasion, and thousands more were wounded. Nazi casualties were estimated at 4,000 to 9,000.