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Although it may have seemed possible, there were many issues that would have prevented it from being effectively utilized. The hose and reel system (drogue) did not offer a rapid fuel flow into the receiving bomber, that's why it was more tailored to smaller aircraft. The refueling boom was a major breakthrough making air to air refueling more effective and practical.It was practical in WWII. A British company called Flight Refueling Ltd. developed a reasonably practical system before the war and the RAF was planning to use the system for refueling Lancs in the PTO. The USAF used an improved version of the system in 1949 to fly B-50 around the world non-stop. I don't know that much about the weight and bulk of the system, but it seems to only have been suitable for large multiengine a/c with aircrew manually connecting the fuel line in the early versions of the system. In addition a single engine a/c with a tractor prop is going to present issues with the prop slicing up the refueling hose. All that being said, I think that if in-flight refueling had been a major r&d priority for the allies, there could have been more practical systems suitable for use by smaller a/c by the end of the war.
I must respectfully disagree with Flyboy. In flight refueling was practical for large aircraft during the war. The hose and reel system was used pre-war to refuel Short Empire flying boats which was a large a/c by any standard. The first generation system required the fueling aircraft to trail a line to the tanker aircraft and then winch back the hose and manually connect it to the fueling system. I don't see this being practical on a smaller aircraft. I think Flyboy overemphasizes training issues. The RAF crews flying in the PTO would presumably have been experienced pilots who could have quickly picked-up the refueling skill sets needed at the same time they were training for long overwater flights. The USAF crews who flew the first non-stop circumnavigation flight had very little training in inflight refueling. While the hose and reel system system was inefficient compared to more modern systems, it was practical and had been used on transatlantic flights. It could reasonably have been expected to have been successfully used by the RAF in bombing Japan. Whether fielding Halifax tankers to Lancaster bombers at a 1:1 or 1:2 ratio would have been practical is another question. The British tended to underestimate the logistical issues of the Pacific war and I'm not sure where they would have parked all of those aircraft.
A couple of basic problems:-
a) Fuel is heavy stuff, I believe around 7ib a gallon, what aircraft can carry that sort of weight once you have allowed for the tanks, pumps, hoses, etc and still carry a decent volume.
b) The receiving aircraft of any type, will need total redesign
c) The impact of all this extra weight on the performance of the receiving aircraft and the payload range of the tanker aircraft.
Training I believe would be possible but it takes a long time and constant practice, even today with all the technology and experience it still goes wrong and pilots wash out because the cannot manage it.