While clearing a section of the Normandy beach near Pointe du Hoc, the crew unearthed a tank that had been buried in the sand since the original invasion. Mechanics cleaned it off, fixed it up and it was used in the movie as part of the British tank regiment.
Henry Grace was not an actor when cast as Dwight D. Eisenhower, but his remarkable resemblance to Eisenhower got him the role.
During the filming of the landings at Omaha Beach, the extras appearing as American soldiers didn't want to jump off the landing craft into the water because they thought it would be too cold. Robert Mitchum (Gen. Norm Cota) was so disgusted with them that he jumped in first, at which point, the soldiers had no choice but to follow his example.
Richard Todd, who took part in the action at the bridge at Benouville (later renamed Pegasus Bridge), was offered the chance to play himself, but joked, "I don't think at this stage of my acting career I could accept a part 'that' small." He was cast as the commander of the bridge assault, Major John Howard, instead. In a strange twist of fate, in one scene of the battle for the bridge, a soldier runs up to Todd, playing Major Howard, and relays information about the battle to him. During the actual real battle, Todd actually did run up to Howard to relay information to him. Therefore, the film actually did show a soldier playing Todd running up to Todd playing Howard and relaying information the real Todd gave to the real Howard.
In his memoirs, Christopher Lee recalls being rejected for a role in the film because he didn't look like a "military man". Despite the fact that Lee had volunteered for the Finnish Army to fight in the Winter War of 1939, before serving in the British Home Guard and later with the Royal Air Force (RAF), RAF Intelligence, the Special Operations Executive (SOE)-- precursor to MI6-- and the Long Range Desert Group (LRDG), which was formed during World War II for reconnaissance missions behind enemy lines and which also provided transportation for the SAS after the SAS was founded by David Stirling in 1941.