I can only assume (my father died several years ago) that he felt somewhat ashamed of his time in the war. I didn't appreciate the negativity surrounding the bombing campaigns until more recently when they opened the memorial in Hyde Park corner in London (http://www.rafbf.org/1794/bomber-command-memorial.html). It's difficult to appreciate this when you grow up watching films like the Dambusters and 633 Squadron and seeing these guys as heroes. Dads are always heroes.