I’ve heard a story of a bomber crew making it back to base even though they had taken some direct hits from anti-aircraft shells which failed to go off. When they got back they located some of these unexploded shells and opened them up to find hand written notes inside saying “this is all we can do”.
Ive read about other instances of the same thing happening but with artilery shells. I think it was shindlers factory in checkaslovakia that prodused the shells.