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Switch Production to the P51
Swipe a few hundred Merlin XXs from the bomber boys for starters.
And several hundred more from Hurricane II production + a longer range version with fuel system a la Mk VII´and VIII
Give the undercarriage a wide track
Switch Production to the P51
after the BOB the Spitfire production should be cut back (produce just enough for an intercepter version to protect UK) to allow for production space for an aircraft that is able to carry the fight to the LW.
Give the undercarriage a wide track