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There were parallel experiments conducted in Europe; at Le Bourget the Aéro-Club de France and the 34th Aviation Regiment of the French Air Force were able to demonstrate passing fuel between machines at the annual aviation fete at Vincennes in 1928.[4] The UK's Royal Aircraft Establishment was also trialling refuelling-in-mid-air, with the aim to use this technique to extend the range of the long-distance flying boats that serviced the British Empire. By 1931 they had demonstrated refueling between two Vickers Virginias, with fuel flow controlled by an automatic valve on the hose which would cut off if contact was lost.[5] The aviation pioneer Alan Cobham bought a patent from David Nicolson and John Lord for £480 each and then developed the probe and drogue method and gave public demonstrations of the system. In 1934 he founded Flight Refuelling Ltd. (FRL), and by 1938 had used an automatic system to refuel aircraft as large as the Short Empire flying boat Cambria from an Armstrong Whitworth AW.23.[3] Handley Page Harrows were used to refuel the Empire flying boats for regular transatlantic crossings
Then Germans with the JU290 and Ju390 were successfully tested. They were to be used to extend the range of their long range aircraft. Would have made an attack on N.America that much more feasible. But divine intervention saw to it this never happened.
The tankers would likely remain inside UK airspace and replace the fuel the fighters burned to reach altitude. That might not extend an early P-47´s range all the way to Berlin but IIRC they could make it to Aachen, so with tankers the Ruhrgebiet might be within fighter range. Good enough for me.
You miss understood Markus. Yes they would have to be based in the UK but what company would build them. Would bomber production be sacrificed to produce tankers?