Battle of Britain.
The film required a large number of period aircraft. In September 1965 producers Harry Saltzman and S. Benjamin Fisz contacted former RAF Bomber Command Group Captain Hamish Mahaddie to find the aircraft and arrange their use. Eventually 100 aircraft were employed, 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 although only 12 could be made flyable. Mahaddie negotiated use of six Hawker Hurricanes, of which three were flying. The film helped preserve these aircraft, including a rare Spitfire Mk II which had been a gate guardian at RAF Colerne.
During the actual aerial conflict, all RAF Spitfires were Spitfire Mk I and Mark II variants. However, only one Mk Ia and one Mk IIa (the latter with a Battle of Britain combat record) could be made airworthy, so the producers had to use seven other different marks, all of them built after the battle. To achieve commonality, the production made some modifications to "standardise" the Spitfires, including adding elliptical wingtips, period canopies and other changes. To classic aircraft fans, they became known as "Mark Haddies" (a play on Grp. Capt. Mahaddie's name). A pair of two-seat trainer Spitfires were camera platforms 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 set dressing, with one Hurricane able to taxi.
For the German aircraft, the producers obtained 32 CASA 2.111 twin-engined bombers, a Spanish-built version of the German Heinkel He 111H-16. They also located 27 Hispano Aviación HA-1112 M1L 'Buchon' single-engined fighters, a Spanish version of the German Messerschmitt Bf 109. The Buchons were altered to look more like correct Bf 109Es, adding mock machine guns and cannon, redundant tailplane struts, and removing the rounded wingtips. The Spanish aircraft were powered by British Rolls-Royce Merlin engines, and thus almost all the aircraft used, British and German alike, were Merlin-powered. [N 2] After the film, one HA-1112 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.
It's not so much that it's a good movie. Off the top of my head I'm hard pressed to think of a "good" war movie. They're all political propaganda in one way or another, even MASH. But it was an amazing piece of filmmaking to go out in the late 1960s and find 75 flyable WWII planes. It's not like they had blue screens or computers.
it's avail on disk via netflix