By the way, here is a little insight into the engineering compartment / radio room machine gun. First the mount.
I found this on "legendsintheirowntime.com" The rack the gun was mounted on was called the "Bell Machinegun Adapter"
From the website:
Kept under cover by censorship until recently, the gun recoil damping device pictured here has been produced in large quantities by Bell Aircraft. It has been used as almost standard equipment on all types of bombers, both British and American.
Consisting of a lightweight cradle of two steel tubes incorporated with hydraulic absorption units, it attaches to the gun very quickly by means of two bolts, meanwhile adding less than an inch to over-all dimensions of the gun and only three pounds to the weight. It is now termed indispensable to accurate fire, and it saves much of the gun mount's structural weight which was formerly necessary to take recoil forces.
After the first of these .50-cal adapters were put into successful operation, a .30-cal mount followed in which the absorption unit consisted of air cushion, springs, and friction disks in place of hydraulic dampers. At present, twin gun mounts for both .30- and .50-cal weapons are being built in addition to single gun units. It is interesting to note that the present .50-cal adapter goes back to experiments conducted with this machine gun on the Bell
Airacuda. The first mount consisted of a steel tube frame connected to two automobile shock absorbers, which were attached to the gun. It worked so well that it served as a basis for the present design, which is very similar in principle.
The device is used on
Liberators,
Fortresses,
Mitchells,
Marauders, Navy dive bombers and torpedo planes, and Martin and Consolidated patrol bombers, as well as on British aircraft and on PT boats. The number required has necessitated formation of a separate ordnance division within the Bell company.
This news clip was originally published in the August, 1943, issue of Aviation magazine, vol 42, no 8, pp 178, 181.
The other thing I found out was that the actual gun mount came in three different designs. The first one looked like a hula-hoop that was mounted on a track which allowed it to be housed above the aft end of the bomb bay area and was used on F and early G models.
Then came the half a hoop mount that was also mounted on a track that allowed the gun to be moved into the compartment above the bomb bay. Also found on G models as I understand it.
Finally there came the mount that was used on G models which were incorporated on the Cheyenne modified bombers which, fortunately for me, was what the bomber I'm working on had.
I tell you what, it wasn't easy finding this picture.
Thanks for following.