The working titles of this film were The Eagle Flies Again and The Eagle Squadron. After the opening credits, there is a written prologue stating: "The Producers wish to express their appreciation to the officers and personnel of the Royal Air Force whose cooperation, under difficult conditions, made possible the filming of the aerial scenes in this production." According to information in the Twentieth Century-Fox Produced Scripts Collection at the UCLA Arts--Special Collections Library, the original story outline for the picture, dated 25 Oct 1940 and entitled The Eagle Squadron, was dictated by producer Darryl F. Zanuck. The Var review also noted that "Melville Crossman," who is credited with "original story" in the onscreen credits, was Zanuck's pseudonym.
       In Zanuck's original story, "Tim Baker" was to be killed at the end: "What we are working towards is a climax where Ty[rone Power] does some terrifically spectacular thing which ends in his death. During the early days of the present war, in fact, a few days after England came into it, Billy Fiske, the American sportsman and pilot, enlisted with the British Air Force. He was killed in defending England against an air raid, and in his last flight brought down three planes before he himself was shot down. We may be able to use this as a pattern for this part of our story." (William "Billy" M. L. Fiske III, an American former Olympian, joined the R.A.F. in Sep 1939, served with distinction and died on 17 Aug 1940 of injuries received during an engagement with German bombers). The scripts collection and a 5 Nov 1940 HR news item both noted that the story was based on the exploits of the American volunteers in the R.A.F. The news item, and another in early Dec 1940, indicate that Henry Fonda, Don Ameche and Mary Beth Hughes were scheduled to appear as the film's stars.
       According to notes from a 25 Nov 40 conference with Zanuck and the production team, the death of "Tim Baker" would mean that an actor other than Power would have to play the part because "the serious objection to Ty would be that audiences would resent his dying at the finish, and not getting the girl." It was suggested that the part should therefore be played by either James Cagney or Fred MacMurray. The ending in which "Tim Baker" is killed was apparently filmed, however, and according to the 13 Sep 1941 MPH review, "the happy ending [was] filmed after early preview audiences protested the killing of the hero at Dunkirk."
       An 18 Aug 1941 HR news item reported that Zanuck had just ordered the new ending to be filmed. According to the scripts collection, however, it was in late Jan 1941 that Zanuck changed his mind about "Tim Baker" getting killed in the end and "Wing Commander Robert Morley" coming to a romantic conclusion with "Carol Brown." Notes from a 31 Jan 41 conference with Zanuck reveal that Zanuck had discussed the problem "unofficially with some British officials," who felt that the lead character should not die because no more deaths should be shown than were "absolutely essential" to the story. The scripts collection and studio publicity note that also planned but deleted was an elaborate wedding between "Tim Baker" and "Carol Brown" at the end of the picture after "Tim" is discovered to be alive.
       Although the scripts collections and the Twentieth Century-Fox Records of the Legal Department, also at UCLA, note that Robert Hopkins worked on a "story outline" entitled The Eagle Flies Again, the extent of his contribution to the completed picture has not been confirmed. A 5 Nov 1940 HR news item notes that Hopkins was working on the screenplay, as was Martin Hudson, whose contribution to the release film has also not been confirmed. According to HR news items, Phillip Reed was tested for a role in the picture, and Ronald Sinclair was also to be included in the cast, but their participation in the completed picture has not been confirmed.
       According to the MPAA/PCA Collection at the AMPAS Library, both the 21 Mar 1941 and 28 Mar 1941 versions of the film's script were rejected by the PCA because of "the inescapable suggestion" of an "illicit sex affair" between "Tim" and "Carol." The PCA also objected to a long drinking sequence in which "Tim and Roger" and shown "staggeringly drunk." The problems were eventually resolved and the picture approved. The PCA file also reveals that by 8 Aug 1941, the film had had three public previews.
       Many contemporary sources remarked on the unusual amount of cooperation received by Twentieth Century-Fox from the British government and military in the making of the picture. According to studio publicity, Lord Beaverbrook, the British Air Minister, was consulted about the story and "expressed the wish that the comedy and romance might lift the film out of the usual category of war plots." Lord Beaverbrook "set the facilities of the Air Ministry at the disposal of the studio," and numerous contemporary sources noted that thousands of feet of film showing the R.A.F. in action fighting against German planes were sent to Twentieth Century-Fox by Britian. According to studio publicity, studio cameraman Otto Kanturek and his assistant, Jack Perry, went to England to film airplane fight sequences and were shot down and killed during a dogfight between R.A.F. and German fliers.
       According to HR news items, Life and studio publicity, portions of the film were shot on location at the Lockheed Air terminal in Burbank, CA, where all cast and crew members were required to submit proof of American citizenship to gain entry. The Dunkirk sequences were filmed on location at Point Magu, near Oxnard, CA, and at an artificial lake on the Twentieth Century-Fox backlot. The sequences, which took either 27 or 28 days to complete, employed over 1,100 extras, most of whom were American Legion veterans, had more than 2,000 special effects explosions and cost between $190,00 and $250,000. Additional shooting was done in Santa Ana, CA. A 14 Apr 1941 HR news item noted that a German Messerschmitt airplane, shot down by the R.A.F. and sent to the studio for inspection and use in the film, was later put on exhibit at Gilmore Stadium in Los Angeles and the proceeds were donated to British War Relief. A 24 Jan 1942 studio press release reported that Lt. Harold Barlow, an R.A.F. pilot used as Tyrone Power's flying double, had been shot down and taken prisoner in Germany.
       Tyrone Power appeared in a special trailer, entitled "Three of a Kind," for the 1941 Twentieth Century-Fox film Charley's Aunt (see above). In the trailer, Jack Benny, the star of Charley's Aunt, sits in the studio café and discusses his film with Power, who comments on A Yank in the R.A.F., and Randolph Scott, who talks about Belle Starr. No scenes of the three pictures were shown. A 8 Sep 1941 HR news item noted that the studio planned an "international broadcast" that would "include an American salute to the R.A.F. in London, and a greeting from the R.A.F. and the American Eagles to the people of the United States." Although details of the broadcast have not been confirmed, HR news items noted that Power and Betty Grable attended the Hollywood premiere at Grauman's Chinese Theatre, at which 10,000 spectators gathered, while New York Governor Herbert Lehman, Mayor Fiorella LaGuardia and Undersecretary of the Navy James Forrestal attended the New York City premiere. The film received an Academy Award nomination in the Special Effects (Photographic Effects, Fred Sersen; Sound Effects E. H. Hansen) category. HR news items noted that in Jul--Aug 1941, pre-production began on A Tommy in the U.S.A., which Zanuck intended as a "companion picture" to the production. That film, which details the training of British pilots at an Arizona flying school, was released in 1942 as Thunderbirds (see above).