Back on to WW2 aircraft that should of been built:
RAF
Spitfire Mk III:
Merlin XX engine,
Clipped wing tips,
Cannon with 120 rpg,
15% more fuel,
New landing gear with widened track and foward rake,
Wheel well covers,
Retractable tail wheel,
Strengthened fuselage,
Increased armour.
400 mph top speed
3,800 feet/minute rate of climb
Whirlwind II:
2x 1,010 hp Pegasus engines (on 100 octane fuel)
40% increase in fuel capacity
Redesigned fuel cross feed system
High activity Rotol propellers