The film endeavoured to be an accurate account of the Battle of Britain, when in the summer and autumn of 1940 the British RAF inflicted a strategic defeat on the Luftwaffe and so ensured the cancellation of Operation Sealion – Hitler's plan to invade Britain. The huge strategic victory of the outnumbered British pilots would be summed up by Winston Churchill in the immortal words: "Never in the field of human conflict was so much owed by so many to so few".
The film is notable for its spectacular flying sequences, echoing those seen in Angels One Five (1952) but on a far grander scale than had been seen on film before. These made the film's production very expensive.
At the same time, RAF Air Chief Marshal Dowding (Laurence Olivier) realizes that an imminent invasion of Great Britain will require every available aircraft and airman and will not allow additional forces to be deployed to continental Europe. Prime Minister Winston Churchill declares the end of the fight in France and the start of the Battle of Britain.
Through a series of vignettes mixing real figures with fictional characters, the movie documents the efforts for the RAF to prepare for and eventually engage in a monumental air campaign to defend Great Britain. Efforts to rapidly train young RAF pilots at first seem to be futile as the British, Commonwealth and Allied pilots do not have the combat experience of their Luftwaffe foes, and are decimated in large numbers. As the attackers switch from Channel raids to attacks on the RAF airfields, the Allied forces begin to recover and fight back. Eventually, “Eagle Day”, the climatic Luftwaffe operation is launched but through an inadvertent attack on London, an RAF reprisal results in Berlin being bombed. In a rage, Adolf Hitler intercedes in the air campaign and orders London to be razed.
With that fateful decision, the fortunes of the Battle of Britain swing to the RAF as London takes the brunt of the German air armada's attacks. The reprieve from the continual bombing of airfield and aviation installations such as the radar picket stations allows the besieged pilots to build up their strength, even allowing the Polish pilots then in training to join the Battle. As the tide turns against a naval invasion of the British Isles, the film ends with the campaign drawing to a close at the end of the 1940 and Churchill's declaration about the "Few" and their role in saving Britain from invasion.
According to a booklet publicizing the movie, Riess had allegedly once met Göring himself during the war. Galland himself acted as a technical advisor for the movie.
The film required a large number of period aircraft. In September 1965 producers Harry Saltzman and S. Benjamin Fisz contacted former Bomber Command Group Captain Hamish Mahaddie to source the aircraft and arrange for their use. Eventually 100 aircraft were employed, a number whimsically called the "35th largest air force in the world. With Mahaddie's help, the producers located 109 Spitfires in the UK, of which 27 were available for filming, although only 12 were in flyable condition. Furthermore Mahaddie negotiated the use of six Hawker Hurricanes, of which three were in flying condition. The film helped preserve these aircraft, including a rare Spitfire Mk II, which had been a gate guardian at RAF Colerne.
During the actual Battle, the majority of RAF Spitfires were of the Mk 1 variety. However, no flyable Mk Is remained, and the producers had to use over nine different marks from different production variants. In order to achieve a measure of commonality, the production made some "standardised" modifications to the Spitfires, including elliptical wingtips, period canopies and various other detail changes. In the classic warbird community, these modified aircraft became known as "Mark Haddies" (in a play on Grp. Capt. Mahaddie's name). A pair of two-seat trainer Spitfires were employed as camera platforms in order to achieve realistic aerial footage "inside" the battle scenes. A rare Hawker Hurricane XII had been restored by Canadian Bob Diemert, who flew the aircraft in the film. Eight non-flying Spitfires and two Hurricanes were available as "set dressing", with one Hurricane able to taxi.
A North American B-25 Mitchell 44-31508, flown by pilots John "Jeff" Hawke and Duane Egli, was the primary aerial camera platform for the aviation sequences. It was painted in a range of garish colours. The markings were primarily intended for line-up references for aerial filming, and to make it easier for other pilots to determine which way the bomber was manoeuvring. When the brightly-coloured aircraft first arrived, at Tablada airbase in Spain in the early afternoon of 18 March 1968, the spontaneous comment from Derek Cracknell, the assistant director, was "It's a bloody great psychedelic monster!". The aircraft was henceforth dubbed the Psychedelic Monster.
For the German aircraft, the producers assembled 32 CASA 2.111 twin-engined bombers, which were Spanish-built variations of the German Heinkel He-111H-16. They also found 27 Hispano Aviación HA-1112 M1L "Buchon" single-engined fighters, which were Spanish variations of the German Messerschmitt Bf 109. The Buchons were altered to look more like correct period Bf 109Es, by adding mocked-up machine guns and cannons, redundant tailplane struts, and by removing the aircraft's rounded wingtips. The Spanish aircraft were powered by British Rolls-Royce Merlin engine, and thus all the aircraft used in the film's aerial combat, British and "German" alike, were Merlin-powered. After the film wrapped, one of the HA-1112s was donated to the German Luftwaffenmuseum der Bundeswehr, and converted to a Messerschmitt Bf 109 G-2 variant, depicting the insignias of German ace Gustav Rödel.
In order to recreate Junkers Ju 87 "Stuka" dive-bombers, the film company acquired four Percival Proctor training aircraft, and converted two of them into 1/2 scale Stuka replicas, complete with a cranked wing, as "Proctukas". In order to duplicate the steep diving angle of the original Ju 87 attacks, large scale models flown by radio control were used. Radio-controlled Heinkel He 111 models were also built and flown to depict bombers being destroyed over the English Channel. When reviewing the footage of the first crash to be filmed, the producers noticed that a trailing-wire antenna was visible; this was explained away by an added cutaway in which the control wires of a Heinkel are seen to be shot loose.
Two of the "Heinkels" and the 17 flyable "Messerschmitts" (including one dual-controlled HA-1112-M4L two-seater, which was used for conversion training and as a camera ship), were later flown to England to complete the shoot. In the scene where the Polish training squadron breaks off to attack, ("Repeat, please"), the three most distant "Hurricanes" from the camera were actually Buchons marked as Hurricanes, as there were not enough flyable Hurricanes to make up the formation. In addition to the combat aircraft, two Spanish-built Junkers Ju 52 transports were used.
Filming in England was carried out at four airfields: Duxford, Debden, North Weald and Hawkinge, all of which were operational during the Battle — indeed, one surviving Second World War hangar at Duxford was actually blown up and demolished for the "Eagle Day" sequence.
Poor weather beset the filming in the UK; in an effort to reflect the cloudless skies over Britain in the summer of 1940, many upward-facing flying shots were filmed in clear skies over Spain, while the downward-facing shots were almost all done below the clouds, over southern England, whose farmland landscape is very distinctive. However the 1940 camouflage was so perfectly recreated it was difficult to see the aircraft against the ground and sky, so a cloud background was used where possible. Only one Spitfire was relocated to Spain to stand in for the RAF defenders.
Another early key scene was the Dunkirk recreation which coincidentally was shot at the beachfront at Huelva, Spain. Only later did the directors find out this was the actual location where the deception known as "The Man Who Never Was" had been carried out. The Nazis were deceived by counterfeit documents purporting that the Allies were planning to invade Sardinia rather than Sicily, planted on the corpse of a drowned man, dressed as a fictitious Royal Marines Officer, Major Martin, who was allowed to wash up on the beach in 1943. Location filming in London was carried out mainly in the St Katharine Docks area where older houses were being demolished to make way for new housing estates. Partly demolished buildings were used to represent bombed out houses and some disused buildings were set on fire. Ironically, St Katharine Docks was one of the few areas of London's East End to survive The Blitz. Many of the extras were survivors of the Blitz. Aldwych tube station, which was used as a wartime air-raid shelter, was also used as a filming location. Almost all the period equipment from the London Fire Brigade Museum was used in the film.
The scenes at RAF Fighter Command were filmed on location at RAF Bentley Priory, the headquarters of Fighter Command during the Second World War. Air Chief Marshal Dowding's original office, complete with the original furniture, was used.
The film includes a sequence which relates the events of 15 August 1940, on which date the Luftwaffe attempted to overwhelm British fighter defences by launching simultaneous attacks on northern and southern England. The northern attack came over the North Sea from bases in Norway and consisted of a force of Heinkel He-111 bombers escorted by Messerschmitt Bf 110 long-range escort fighters. The attack was subjected to a robust defence from the Spitfires of No. 72 Squadron RAF, and suffered heavy losses, prompting the Luftwaffe to abandon daylight strikes against Britain from Norway. The film's producers did not have access to Bf 110 aircraft, or suitable replicas, and instead the Heinkels are described as being unescorted, with the Luftwaffe reasoning that "even a Spitfire can't be in two places at once."
The Robert Shaw character "Squadron Leader Skipper" is based loosely on Squadron Leader Sailor Malan, a prominent South African fighter ace and No. 74 Squadron commander during the Battle.
The scenes in the operation centre in which the British listen to their fighters' wireless transmissions is for dramatic reasons only. In reality, the operations centre received information on the progress of the air combat by telephone from the sector airfields.
The scenes at the end of the film, where the RAF pilots are seen suddenly idle and left awaiting the return of the Luftwaffe raids is more cinematic license; the Battle of Britain gradually fizzled out through late September, although further daylight raids continued for some weeks after the large 15 September engagement. 31 October is regarded as the official end of the Battle of Britain on the British side.
The confrontational scene between Dowding, Park, and Leigh-Mallory is entirely fictitious. There were tensions between the two sector commanders, but not on this scale. The film doesn't go on to mention that shortly following the end of the Battle, both Dowding and Park were replaced by Sholto Douglas and Leigh-Mallory respectively, despite their having proved that Leigh-Mallory's 'Big Wing' theories were unworkable.
Dowding was a Scot; Laurence Olivier was unaware of this, though since Dowding was educated at Winchester College, it is unlikely he retained an accent (Dowding met Olivier on the set of Battle of Britain, as shown in a documentary present on the UK DVD release; as such, Olivier was familiar with Dowding's actual voice).
One major omission is at the end of the film, when casualties from both sides are listed. The film does not mention losses suffered by Corpo Aereo Italiano, an Italian expeditionary force that took part in the Battle of Britain (albeit from November 1940, after the officially recognised end of the battle). In fact, Corpo Aereo Italiano is not mentioned at all during the film. One entry in the casualty list is a lone pilot from Israel in the British protectorate of Palestine.
There was no attempt to recreate the effect of tracer ammunition.
Göring's train in the film is actually a Spanish one and not a French one and the steam locomotive hauling it is of a class that did not come into service on the Spanish National Railways until 1951.
For the opening credits, Goodwin composed the Aces High March in the style of a traditional German march in 2/4 time. The march places heavy emphasis on the "oom-pah" sound of tubas and lower-pitched horns on the first and second beats and has the glockenspiel double the horns in the melody. Because of the great length of the credit sequence, which involves a general's inspection of a newly-occupied airbase in France, the Aces High has three separate bridges between choruses of the main theme. American radio personality G. Gordon Liddy has used the march as bumper music on his syndicated radio program.
The use of actual aircraft in flying sequences has led to a number of subsequent productions utilizing stock footage derived from the Battle of Britain: