I remember David Putman saying in an interview shortly after Memphis Belle was released that he originally wanted to make a film about a Lancaster Crew but no British backers (City Banks) were interested, But when he came back with the Memphis Belle script they all jumped at it.
I think if you look in the small print of the "Lend - Lease agreement", it states what all films must show the good old US of A winning the war. How must Russians must feel, 20 million dead ( and that's the conservative estimate!). At least Two/Thirds of Germany's forces were permanently committed to the Eastern Front. Most Germans viewed North Africa, Italy, Normandy etc.... as side shows