While researching the immediate post-war Soviet Airborne Units, I discovered the detailed conversions of the Tu-4 bomber into airborne transports.
They developed the Tu-4D and associated "cabins" (giant drop tanks), and Factory no.23 converted 100 to 300 (sources differ) Tu-4 into this configuration starting 1955.
early test of a P-90 cockpit with ZIS-2 cannon
When equipped with two loaded cabins, each with either a SD-44 self propelled gun, or a ASU-57, the Tu-4D had a 800~ km (500 mile) radius of action.
Apparently the system was only in service for a very short period of time -- 1956 to about 1958 -- because at this point the turboprop powered An-8 and An-12 arrived with "roll off" cargo doors.