While the story of the Bloody 100th is perfectly true, Twelve O'clock High was actually based on events in another unit...the 306th, where a Savage-like new commander came in to rehabilitate a broken unit. Bartlett and Lay tripled the Group's number to get the 918th for the book.
Twelve O'clock High is yet another war movie that alters the ending of the source material to make a "punchier" ending. In the book, Savage's breakdown has primarily physical impacts...his mind won't let him climb into the airplane, but doesn't have the mental confusion and near-catatonia that Peck shows in the movie. This was a deliberate decision by the film-makers, and I can't argue that it doesn't make the film more powerful. The book actually ends with Savage driving peacefully away, to a new assignment.
The Blue Max departs from the source material even further, with the Staffel commander, not Bruno Stachel, dying in the new monoplane. The book ends with him being blackmailed by the Countess to be her toy (and who, sadly, is no Ursula Andress).
C.S Forester never wrote a happy ending his life, hence, war movies based on his books almost always changed at the end. You can just see the producers say, "No, no, the audience expects something else...." They had to combine three Hornblower books to come up with one with a happy ending (and the third book ends with Hornblower learning his wife is dead), "Brown on Resolution" (aka "Sailor of the King") ended with the titular sailor actually living, "The Pride and The Passion" (aka, "The Gun") actually had to add a character so one of the main characters was actually LIVING at the end.
And I can just imaging John Huston at a script conference for "The African Queen." "***** no, they're going to SINK that Hun gunboat!"
Ron Wanttaja