From what I know, the Germans had mastered the techology of drop tanks in 1936 or so.
The Brits were a tad slower, after all their policy was home defence.
To think of it, the Spitfire could easily have had the range of the P51, but for most of the war only the PR units were blessed with that.
So, basically, I am quite amazed that both nations even tried this. This is just so bloody silly compared to a DT!!!!!