Field Marshal Erwin Rommel's (Werner Hinz) son, Manfred Rommel is played by Michael Hinz, the real life son of Werner Hinz.
First film of Siân Phillips.
Former U.S. President Dwight D. Eisenhower was considered for the role of himself in the film, and he indicated his willingness. However, it was decided that makeup artists couldn't make him appear young enough to play his WWII self.
Four Spitfires were used in the strafing sequence. They were all ex-Belgian target tugs and all were MK9's. The serial no.s were MH415, MK297, MK923 and MH434 and all are still extant. The Spitfires were assembled and co-ordinated by former free French Spitfire pilot Pierre Laureys who flew with 340 Squadron, a free French unit in the RAF. The 4 Spitfires were of course re-painted in 340 Squadron markings. Spitfire MK923 was between 1963 and 1998 owned by film actor and Oscar winner Cliff Robertson.
In 1963, Black civil rights organization the NAACP accused Hollywood studios of racial discrimination. Using 'The Longest Day' as an example, it said that there were some 1,700 black soldiers who took part in the actual landings, but this movie featured not a single black actor.
In his memoirs Christopher Lee recalls being rejected for a role in the movie because he didn't look like a military man (he served in the RAF during WW2).
In Italy for the filming of Cleopatra, Roddy McDowall became so frustrated with the numerous delays during its production, he begged Darryl F. Zanuck for a part in this picture just so he could do some work. He ended up with a small role as an American soldier.
In researching his contribution to the script, Romain Gary uncovered one of Cornelius Ryan's mistakes: the casino at Ouistreham had not existed on June 6, 1944. Since the casino set had already been built, however, the scene taking place there was filmed anyway.
In the Spanish version, actors Fernando Rey and Jesús Puente dubbed actors Henry Fonda and Peter Lawford.
Just before shooting began in Corsica, Darryl F. Zanuck was approached by a man stating he represented the beach owners. He insisted on a $15,000 payment or else they would drive modern cars along the beach. Zanuck paid the money, but it was later discovered to be a scam as there were no private beaches in Corsica. Zanuck eventually won damages after an eight-year lawsuit.
Many of the beach scenes were filmed in Corsica.
Many of the military consultants and advisers - drawn from both sides - were actual participants on D-Day itself.
No gliders of the sort used in the invasion were available, so Darryl F. Zanuck commissioned new duplicates from the same company that built the originals.
One of producer Darryl F. Zanuck's big worries was that, as filming of the actual invasion drew near, he couldn't find any working German Messerschmitts, which strafed the beach, or British Spitfires, which chased them away. He finally found two Messerschmitts that were being used by the Spanish Air Force, and two Spitfires that were still on active duty with the Belgian Air Force, and rented all four of them for the invasion scenes.
One of the uncredited writers on the film was James Jones, author of "From Here to Eternity".
One of the very first World War II films made by an American studio in which the members of each country spoke nearly all their dialog in the language of that country: the Germans spoke German, the French spoke French, and the Americans and the British spoke English. There were subtitles on the bottom of the screen to translate the various languages. There were two versions of this movie, one where all the actors spoke English and the other(the better known one) where the French and German actors spoke their respective languages.
Only 6% of the paratroopers depicted actually achieved their goal. 60% of the men and equipment parachuted in on D-Day was lost.
Producer Darryl F. Zanuck paid the original author Cornelius Ryan $175,000 for the screen rights to his book.
Pundits nicknamed the film "Z-Day".
The biggest grossing black and white film up until the advent of Schindler's List.