The FN64 was useless for night ops,as the gunner did not have direct vision,as I said in an earlier post some crews did have a ventral scare gun (esp the canadians).
Unfortunately the H2S installation precluded refitting a turret in that posn,so a scare gun was the only real option.
The feeling I get from reading Bomber crew autobios is that the majority of the RAF main force crews had no knowledge of upward firing nightfighters,the canadians seeming much more concerned about the obvious vulnerability of underbelly attacks.
rgds LR