Why did reviewers of Catch-22 at the time of its publication in 1961 describe it as "shocking"?

I think that it satirized war in a way that had not been done before. It kind of reminded me of the book MASH and its subsequent TV series. The humour in Catch 22 is dark but quite entertaining. I think the characters were so unique yet at the same time made statements about the war (WW2) that were so profound. There was the character of Milo Minderbinder, a dedicated entrepreneur who bombs his own airfield when the Germans offer him an extra 6 percent. Some adjectives used to describe the book have been clever, subversive and cathartic.