jb2 86uk
I know that there were trials at Farnborough towards the end of WWII involving Spitfire in vertical dives. The indicated speeds were close to M=1. However, at that time there were lengthy pipes between the static pressure head and the recording instruments, and at that time our knowledge of the resulting pressure lags was limited, and in steep dives could be appreciable. The Spitfire wing had a higher critical mach number than the Meteor, because of a thinner wing section