The Amaurotean Capitalist wrote:

"Scott M. Kozel" wrote:

You keep calling it a "Merlin-engined Mustang"

Because it used a Merlin engine. QED.

No, it used ---

while in fact those
built by NAA utilized a Packard built engine that was a modifification
of the Merlin design.

The Merlin 61 used in the initial Spitfire IX's was also a
modification of the Merlin design. The fact remains that the V-1650-3
and -7 were two-stage Merlins produced under licence by Packard.

That is partially true. Packard modified the turbocharger to produce
more high-altitude power, and modified the alloys of some of the major
engine components to adapt the engine to U.S. mass production
engineering and processes. The Rolls-Royce Merlin engines were hand-
built. U.S. mass production processes allowed vastly greater
quantities (over 16,000) of the V-1650 to be built in a timely and
reliable manner. Packard added considerably to the design of the
engine, which includes and is integral with its production processes.

If there was no P-51 then North American would have been producing
more B-25's at their Dallas plant and probably at Inglewood as well.
Which leaves the US with what they had at the time; the P-38, the
P-39, the P-40 and the P-47. Now which of these are you going to stop
production of in order to develop a better long-range fighter design?
The longer-ranged P-47D doesn't come along until April 1944 (and
requires that British Typhoon tear-drop canopy in any case), the
dive-brake-equipped and longer-range P-38L doesn't appear until May
1944, and neither the P-39 nor the P-40 are ever going to become
high-performance, high-altitude long-range fighters.

If there was no P-51 then some U.S. company would have greatly
accelerated the production of something of similar performance. Most
likely an advanced P-38 and/or P-47.

Both the U.S. and the British each produced a number of excellent
advanced warplanes in WWII. In a universe without the P-51, certainly
something else of similar performance would have been produced.