"Keith Willshaw" wrote in message
...
Given that the RAF had a number of B-17's complete
with ball turrets I rather think the idea was not completely
unknown.

Would it really have helped anyway? AIUI ventral ball turrets were very
uncomfortable and in day bombers, gunners moved to them only when fighters
were detected. Besides ventral gunner is still in enormous disadvantage
against a night fighter, he doesn't have a radar and night fighter can see
the bomber easier against the sky.