While I understand the push-back on that terminology, I believe a it's fair phrase to apply, though undoubtedly the language is slightly hyperbolic in the case of the Spitfire. Attached are the range specifications for a typical P-47C, ranging from the C-1 to C-15 sub-blocks. On internal fuel, the aircraft is loaded with 305 US Gallons at a take-off weight of approximately 13,500-lbs. This provides the following:
P-47C: 305 US Gallons internal, 13,500-lbs take-off weight,
650-miles range at Maximum Cruise power, or
400-miles at Maximum Continuous power (
325-miles at low altitude).
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If we compare to the contemporary P-40 series (excluding the P-40L and P-40N-1, since both are assuredly inferior in range due to their ~20% reduction in internal fuel capacity). we have the following information:
P-40F: 157 US Gallons internal, 8,850-lbs take-off weight,
600-mile range at Maximum Cruise power,
425-miles at Maximum Continuous power (
375-miles at low-altitude).
P-40K: 157 US Gallons internal, 8,800-lbs take-off weight,
600-miles range at Maximum Cruise power,
350-miles at low-altitude Maximum Continuous (no data-point for high-altitude)
P-40M: 157 US Gallons internal, 8,800-lbs take-off weight,
550-miles range at Maximum Cruise power,
475-miles at Maximum Continuous power (
325-miles at low-altitude).
View attachment 806486
Yes, there is subject to fine interpretation with each of these individual values, but I believe it does relay my position of "about on-par" adequately. While reasonable minds can disagree on where the line is for "about on-par", or what meets that metric, in my perception of the ranges of both aircraft are within a fairly narrow margin of difference--before later P-47 models are introduced, and become prolific in their carriage of large underwing tanks.
Information comes from the tactical planning charts for each aircraft type, unfortunately no data was present for the later P-40N models, otherwise I would've included them as well.