The government commissioned Olivier to make a film that would prove inspiring to the beleaguered British people who were then suffering through their 5th year of war with Germany.
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).
The most significant cuts to the text - the ones which generally provoke criticism at Henry as a king - were reputedly made at Winston Churchill's request.
The only lines in the film not written by Shakespeare are spoken by Pistol at the end of the Boar's Head scene: "Farewell, farewell, divine Zenocrate/Is it not passing brave to be a king/And ride in triumph through Persepolis!" They are from "Tamburlaine the Great" by Shakespeare's contemporary, Christopher Marlowe.
The opening model shot of London was huge - 50 x 70 feet in size and made of plaster. It took 4 months to construct.
This is the only one of the three Olivier-directed Shakespeare films in which the full title of the play was used in the opening credits.
When Vivien Leigh, originally slated to play Katherine of France, was forced to give up the role, Renée Asherson replaced her because she was exactly the same size as Leigh and therefore the costumes didn't have to be altered to fit her.