There was only one catch and that was Catch-22, which specified that a concern for one's safety in the face of dangers that were real and immediate was the process of a rational mind. Orr was crazy and could be grounded. All he had to do was ask; and as soon as he did, he would no longer be crazy and would have to fly more missions.
Real Catch-22 they set up there
That's some catch, that catch-22
“But what if all the other soldiers wanted to desert too?”
“Then I’d be a damn fool to think anything else!”