Sir William Walton was first hired to write the score, which would have been his last. Because of his advanced age, he turned to friend Sir Malcolm Arnold for assistance with the orchestrations (which Arnold supplied, as well as writing additional cues). Producer Harry Saltzman rejected the score, stating it wasn't long enough. Ron Goodwin was hired to write a new score, but when told he would be replacing one of Walton's, his first reaction was, "Why?" Goodwin eventually wrote the replacement score, but Laurence Olivier threatened to have his name removed from the credits if none of Walton's original was used. For this reason, Walton's original music was kept for the "Battle in the Air" sequence towards the end of the film.
The character of Section Officer Maggie Harvey is based on Air Commodore Dame Felicity Peake, who was a young section officer at RAF Biggin Hill in 1940. The scene of Harvey being ordered to put her cigarette out, and Harvey yelling back Warrant Officer Warrick, was based on a real event.
The character that Harry Andrews plays is called Senior Civil Servant in PR and cast lists. He is called Sir Austin Stokes in paperwork regarding the film production.
The closing credits cite the following statistics relating to the number of pilots / air force personnel (AFP) from various countries who took part in the Battle of Britain and the number from each country who were killed in action (KIA): American (AFP: 7; KIA: 1); Australian (AFP: 21; KIA: 14); Belgian (AFP: 26; KIA: 6); Canadian (AFP: 88; KIA: 20); Czech (AFP: 86; KIA: 8); Fleet Air Arm of the Royal Navy (AFP: 56; KIA: 9); Free French Forces (aka Forces Françaises Libres, FFL) (AFP: 13; KIA: 0); Irish (AFP: 8; KIA: 0); Israeli (AFP: 1; KIA: 0); New Zealander (AFP: 73; KIA: 11); Polish (AFP: 141; KIA: 29); R.A.F. (Royal Air Force) and other Commonwealth (AFP: 1822; KIA: 339); South African (AFP: 21; KIA; 9) and Southern Rhodesian (AFP: 2; KIA: 0). These figures total to 446 people killed in action (KIA) from 2365 pilots / air force personnel (AFP).
The Heinkel 111 as shown in the movie had only three 7.92 machine-guns total. To the rear, front and belly. A common criticism of the HE111 during the actual battle of Britain was that it was inadequately armed to deal with the enemy fighters. Later models added left and right machine-guns.
The Heinkel 111 bombers were in fact Spanish built CASA 2111 bombers, Heinkel 111 H constructed under license, but with Rolls-Royce Merlin engines and many other modifications. The Rolls engines were more powerful than the original Junkers Jumo and so the planes had more performance. In fact, all the real airplanes used on the film, except the Junkers Ju 52 (also Spanish built CASA 352) had British-built Rolls Royce Merlin engines.
The Jackdaw Inn, located in Denton near Canterbury, Kent, features in scenes based around the first on-screen meeting of Colin and Maggie Harvey - Christopher Plummer and Susannah York. It also serves to place the event in historical context of the story with a muster of the Local Defence Volunteers (LDV) outside.
The Junkers 87 Stuka dive bombers used in the film are model airplanes filmed in Malta, the only ones not real (the Percival Prentice aircraft which had been modified to represent Junkers 87 aircraft were found to be too dangerous to use). Their dive-bombing technique is not very real: Stukas will usually dive to 60-90º and release their bombs while diving (not pulling up).
The large number of aircraft collected for this production made it the 35th largest air force in the world.
The movie lost $10 million worldwide.
The number of German losses (i.e. killed in action (KIA)) during the Battle of Britain are tabled during this movie's closing credits. Bomber Crews KIA: 1176; Stuka Crews KIA: 85; Fighter Bomber Crews KIA: 212; Fighter Pilots KIA: 171; Missing Crews, believed to be KIA: 1445. Therefore, according to this movie, German losses from the Battle of Britain amounted to 3089.
The planes used as Bf 109s were actually Spanish Hispano HA-1112 Buchons. Basically a Bf 109 with a Rolls Royce Merlin engine, the nose of the plane looks completely different that of a German Bf 109.
The recently closed St Katherine's Dock was used for some of the bombing scenes, the site of the warehouse is now a hotel. At the time of filming, only that dock had closed in London and it had been badly damaged during the blitz.
The scene of Göring accusing Kesselring of betrayal as his train departed was based on a real event. In the actual event Göring had left in such a hurry that electrical and telephone wires between train and the station building were left connected. These were broken and left trailing from the carriage when the train departed. Director Guy Hamilton had wanted to include this in the scene but thought it would look too comic.
The scenes at Fighter Command were filmed on location at RAF Bentley Priory, the actual headquarters of Fighter Command during WW2. Air Chief Marshall Dowding's original office complete with the original furniture were used.
The Spitfires, Hurricanes, Messerschmitts and Heinkels were repainted into authentic 1940 colors, but were so perfectly camouflaged that they could not be seen against the ground or sky. Most of the aerial scenes were filmed with cloud in the background so the aircraft could be seen.
The white "smoke" from damaged engines was made by injecting cooking oil into the exhaust manifold.
There were to have been scenes featuring Lord Beaverbrook. Alec Guinness was hired to play Lord Beaverbrook, but these scenes were cut from the script shortly before filming.
This film became regarded as a patriotic tribute to "the few," that many of those involved in the production, actors and technicians, reduced their normal fees to work on this film. Much of the large budget went toward the acquisition, restoration, modification, maintenance and operation of the vintage aircraft.
This film's closing epilogue is a famous quote from Winston Churchill. It states: "Never in the field of human conflict was so much owed by so many to so few" 'Winston Spencer Churchill'. In some versions of the movie, the quotation differs from the above mentioned and instead reads "This is not the end; it is not even the beginning of the end, but it may be the end of the beginning." Of course, this quote is also being attributed to "Winston Spencer Churchill".