I believe it was the Canadians who were the first to re-fit a ventral gun, after they became convinced of the reality of ‘schrage musik’, which Command was still in denial about. That would be late in ’44.

Incidentally, I read once that the .50 gun was the prefered weapon of the RAF when they were considering the replacement of the Gladiator. At a meeting in ’32/’33 (can’t remember which) the Treasury insisted that .303 guns would have to be used because there were millions of rounds of .303 ammo left over from WWI that had to be used up before a change of calibre could be considered. Does anyone know any more about that?