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Don't know of any testing, or even a consideration. I would have thought the structural requirements, plus the weight, would have been a major issue, and that's before the extra crew member, and ammunition, not to mention logistics (at that point in the war. The Martin turret arrived late in the proceedings).
Didn't the Halifax in some Groups have belly guns?
no need for Sperry
ED
EDIT: I'd be interested see a close-up pic or diagram which showed the FB25 turret - my cursory internet search couldn't find anything.
Axis History Forum • View topic - Wartime British Remotely Controlled Guns and Turrets
remote controlled 20mm upper and lower turrets
I think that was just another way of saying the gunner would have very little chance of seeing a fighter approaching from below at night, until it opened fire.The RAF 100 Group had a small no of B17s which were used at night. These were of course equipped with the Sperry ball gun but they were removed after a few months of service as they were impractical at night. However I don't actually know what they meant by impractical. It wasn't beacuse of any weight problems that I do know.
RAF learned about the threat a year or two after Luftwaffe put it (S. musik) to a good use...
The RAF 100 Group had a small no of B17s which were used at night. These were of course equipped with the Sperry ball gun but they were removed after a few months of service as they were impractical at night. However I don't actually know what they meant by impractical. It wasn't beacuse of any weight problems that I do know.