This is a well-researched and written book: Thomas KcKelvey Cleaver is a screenwriter and World War Two air war historian. It was recommended to me, in part, for perspective on the novel Catch-22.
Air combat in the Mediterranean was not as predictably fatal as it was for the heavy bomber crews operating out of England. That said, the Brenner Pass was. A B-17 crew member operating out of England could rotate home after 25 missions. The number of missions required of Heller's Wing went from 60 to 70 and then "for the duration" (right before the end of the war). This was because of a shortage of replacement crews after mid-1944.
It had not occurred to me that a tight bomb pattern was mission-critical. It was well-established, even during the war, that so-called strategic bombing in France and Germany was inaccurate. In Catch-22, Colonel Cathcart insists on a "nice, tight, bomb pattern that will look good in the aerial photographs" so he can be promoted. Actually, to take out bridges and rail lines, tight bomb patterns were a necessity.
And now, to fly into flak-infested skies:
Cleaver establishes that Heller flew "only" 60 missions, when the number had been raised to 70 (and later "for the duration.") Devotees of Catch-22 will recall that never-ending increases in the number of missions drive the plot of the book. Heller flew no missions in his last month on active duty, and was rotated home at a height of operational tempo in December-January 1944-1945. Heller was eligible for separation based on the complicated "points system" the Army used: time-in-theater, number of missions flown, etc. But Heller was 10 missions short of what General Robert Knapp required.
Cleaver says that Knapp was the model for General Dreedle in Catch-22. Maybe. Heller's sketches of "General Dreedle, who ran a fighting outfit..." and his bureaucratic wars with General Peckem are consistent with that. But in Catch-22, it's Colonel Cathcart who continually raises the number of missions in an effort to impress Dreedle. The characters in Catch-22 are inventions and composites. Further, Heller has observed that the themes, and tone and sensibility, of Catch-22 are more about the 1950's than World War Two. And that his own experience of the war was limited and that he, personally, enjoyed everything about the Army until the last two months or so of his service. He said that he didn't have the sense to be scared until the Avignon mission. (Here's the link, again, to his appearance with Kurt Vonnegut and Stephen Ambrose. Heller was 72 at the time and his perspective was retrospective.) https://www.c-span.org/video/?65129-1/battle-bulge-ve-day
In the appearance linked to, Heller says that he "arrived in the squadron at just the right time for me:" tough missions against Monte Cassino were in the past and tough missions against the Brenner Pass were in the future. Fifty-eight of Heller's 60 missions were against bridges with no Axis fighter planes and little flak. His first 37 missions were "milk runs." He found his (much later) reading about the losses of the Eighth Air Force heavy bombers appalling: 60 planes (600 crew) lost on the Schweinfurt mission alone.
The mission to the Avignon bridges (August 15, 1944) woke Heller up to the fact that he was in combat. A fictionalized but realistic account of Heller's experiences at Avignon appears in Catch-22. Besides the pilots' evasive action, and his own mic jack being disconnected, a crew member received a leg wound from flak, which Heller helped to treat. In the novel, this crew member is transformed in to Snowdon. The Settimo Bridge mission (August 23, 1944), which Heller also flew, to create a road block with a land slide by attacking a village, also figures in Catch-22. Cleaver believes it was the pivotal point in Heller's disenchantment with the war.
Cleaver uncovered the fact that, for his last month or so in-theater, Heller was detailed to the making of a film to promote the Bomb Group's (and its commanding officer, Colonel Chapman's) record. Training In Combat was about training replacement crews, the absence of which required increasing the number of missions. The film-maker recruited Heller, a friend, to play the part of "Pete the bombardier." He referred to his film as "the Colonel's boondoggle." This sounds like the Colonel Cathcart we know from Catch-22. Hyping the training of non-existent replacement crews is straight out of the novel's sensibility, too.
Cleaver speculates that Heller did make a deal with Colonel Chapman, the one that Yossarian rejects in the novel. Heller would stop grousing about the increased number of missions if he didn't have to fly them. He even got sent home. Cleaver believes that Heller had "a well-developed personal conscience," which bothered him, and which (in part at least) inspired Catch-22. Yossarian is Heller's avatar--the Heller who did the right thing. Heller died in 1999, long before Cleaver uncovered the boondoggle film, so we can't ask him.
Having read biographical material about Heller, and contemplated his other novels and public appearances, I'm not persuaded that his personal conscience was any more well-developed than average, if that. With the possible exception of Dunbar, the characters in Catch-22 are not stand-up guys. Many of them are not even "characters," in the conventional novelistic sense: they don't "develop." Some are two-dimensional personifications: Milo Minderbinder stands in for capitalism, for example. What Heller did have was a superb nose for hypocrisy. He could smell it from miles away. For me, hypocrisy is the theme that drives Catch-22.