I was also aware of 0.5 machine gunned turrets, I may be wrong but I thought that this was a local modification on 5 Group aircraft based in and around Lincolnshire. The modified turret was called a "Rose turret" after the engineers Rose of Gainsborough who were the engineers responsible. The RCAF 6 Group based in Yorkshire did something similar with a local modification of a single belly mounted machine gun as they suspected the existence of night fighters equipped with upward firing armament, in fact they were quite correct as the Luftwaffe had two upward firing cannon called Schragen Musik.