"Seems we just gave the illusion of self defence at the expense of 3 extra "crew" that just sat in their turrets trying to penetrate the darkness."
because bombers always had defensive weapons ... in WW1.
No-one was willing to change things even though it was obvious that at night and +200mph the chances of a successful shoot down were near zero
Fixed guns in the nose and an observer at the back would have made a lot more sense until radar controlled guns came in - and then you'd want something serious not a set of 0.303's