Prince Niccolo,
The Rose turret fitted was a modification to increase the firepower.
The turret has 2x 0.50cal MG fitted.
Here is the link with all the info-
Rose turret - Wikipedia, the free encyclopedia
The museum also has a B24 turret with 2x 0.50cal MG. They are both very small inside and only a small framed and shortish man had any hope of fitting in them!!
The 0.303 MG was not considered adequate as the war progressed.
Most fighters of the later war on both sides had either 0.50cal MG and /or 20mm cannon fitted.
Armament on some German night fighters included 2x 30mm mk108 cannons that fired obliquely upward into the undefended belly and fuel tanks of British bombers. ( No ventral turrets).
Devastating firepower with HE shells. Just 1or 2 strikes could easily set a fuel tank ablaze or turn an engine into scrap metal!!
Very Brave men indeed to do that job night after night against incredible odds!!