Just to add to the thread, whilst not a Hercules per-se the L100 we used in Afghanistan regularly moved fuel using internal fuel tank.
We flew on average 6 days a week into many bases, some known and some people didnt know about.
2nd mission into Tarin Kowt 12 months after the Australians pulled out and we took small arms fire in port wing and ramp. Patched it up and flew back to Kandahar but patch failed coming into landing which made for interesting time.
15,000ltr fuel tank with filter/pumpset to offload.
Farah Airfield where previous night US Special Forces had taken over the airfield and we fly in to deliver fuel into the bags.