I disagree. Sorry. Range is coming from order from Air Ministry. Ministry specify what data should new fighter fullfill. If only short or medium range is presribed, fighter will designed for short or medium range. If long range presribed, fighter will designed with long range. Simple.
Quite right. Designers seldom told air staffs what to order. they could present an idea and see if the air staff went for it but that was about it. Air staff wasn't going to pay for anything they didn't OK.
P-47 bad example. Very bad. P-47 - same role as Spitfire, 109. Interceptor. Range no better than 1939 Spitfire or 109. Later improved, but only by putting extreme amounts of fuel. Still not very long range for task.. Very stupid plane IMHO. But it is not fault of designer... designer was told to design such plane.. it is fault of planner. Why would US need interceptor - like if there were serious bomber threat to US...? In 1939..? No bomber had range.. until post war.
That is easy to see in hindsight. It was not so easy to see at the time. the American spy or intelligence system may have been a little lacking.
But the US planner//s knew what they were planning. The B-29. They knew what they had built already, the B-15 and B-19 bomber prototypes. They had an idea of what was technically possible even if it turned out not to possible in large scale production.
Not to build the P-47 was to gamble that the Germans and Japanese could not/would not build long range/ high altitude bombers just like the US was planning to build. The bombers needed more time to bring to operational status than the the single engine fighter but for a number of unforeseen reasons. Granted any large complex aircraft is going to have more problems than a small one but the B-29 seemed to have more than it's share.
Betting the Germans COULD NOT come up with something would have been seen as irresponsible if they had.
The British were able to bomb Genoa Italy from England using Whitleys, not the most advanced bomber in the world, in June of 1940. Most Military planners were also vastly over estimating the effectiveness of the size of bomb loads at the time. A bomber that carried 2000-4000lbs of bombs was seen as a very effective threat rather than a large nuisance.
The P-47 may not have been designed to defend the Continental US. In it's radial engine form it was designed with lessons from the BoB (not 1939). With combat taking place in 1940 at 25,000-30,000ft, at what altitude was combat going to take place in 1942-43 regardless of what airfield/country the plane is flying out of?
Again it turns out that combat didn't much higher than 25,000-30,000ft but who knew that in 1941-42? Certainly not the Germans who spent time and money on Pressure cabins, NO2 systems, Turbo charged diesel Reconnaissance/bomber planes, and planes with fuselage mounted engines to supercharge the wing mounted engines.
With eight .303s proving less than desired in the BoB what should they have specified in armament? for fighter to go into service more than two years in the future?
A single 20mm and two .30cal MGs??
They knew they had 2000hp engines, they knew the British had 2000hp engines (3 of them in the works) How were they to know that the Germans would drop the ball and NOT develop a working 2000hp engine by 1942/43?