Backed by the Pentagon: Many of the 'casts of thousands' extras were servicemen, and it is said that you can tell the American servicemen as they wear their helmets at a jaunty angle.
California Doubling: The majority of the film, including the Battle of Agincourt, was filmed in Ireland where cast and crew could be safe from nightly Luftwaffe raids (Ireland was a neutral country in the Second World War).
Max Adrian, who portrayed Louis The Dauphin was 41 years old at time of production, whilst the real life character he portrayed was only 18 years old on October 25, 1415, the date of the Battle of Agincourt.
Princess Katherine was approximately 14 years old at the time of The Battle of Agincourt, however, Renée Asherson was approximately 29 years old at the time of production of the film, more than twice the age of the real life character Asherson was portraying.
No Stunt Double: Due to the absence of trained stunt men, Laurence Olivier had to do his own stunts as well as showing almost every Irish extra how to do their stunts (this resulted in him suffering many injuries including fractured shoulders).
Reality Subtext: The film was partly intended as a wartime morale-booster for the British. Certain parts of the play were consequently omitted, such as Henry's hanging of a friend as an example of firm justice.
Olivier's then wife, Vivien Leigh, very much wanted to play Katherine, but David O. Selznick would not let her out of her contract with Selznick International Pictures, feeling that the role was much too small for an actress of her cache. Leigh never forgave Selznick, and never worked for him again.
John Gielgud asked Olivier to cast him as the Chorus, but Olivier declined, offering him the lesser role of the King of France instead. Gielgud turned down the offer.
Enforced Method Acting: Kenneth Branagh said in an interview that carrying the "corpse" of Christian Bale caused him terrible back pain. He carried his dead weight for the whole of a long tracking shot. The look on his face was genuine pain and not acting.