laminar to turbulent

Actually, I doubt WWII aircraft obtained much laminar flow at all due to matt camouflage paint applied to the surface, skin joints, and rivets. It's really been the advent of composite light aircraft and sailplane structures that have made it routine to achive large amounts of laminar flow.

Even without laminar flow the NACA 6-series sections have been a success, however. Because skin friction is proportional to velocity squared, the rooftop pressure distribution of the laminar flow sections worked well to lower turbulent profile drag. And the linear pressure recovery pressure distribution of the NACA 6-series airfoils resulted in measured growth of trailing edge separation with angle of attack and a gradual stall. (At low Reynolds numbers, the NACA 6-series airfoils are prone to leading edge stall due to laminar separation triggered by the leading edge suction peak, but this wasn't such a problem at fighter Reynolds numbers.)