What was the first supersonic wind tunnel?
The world's first supersonic wind tunnel started operating in National Physical Laboratory in Teddington, England in 1922.

It basically used a pressure tank upstream, which was used to generate supersonic flow in a cross section of 20.3 mm, which was used to study projectiles.

From the book Aeronautical Research in Germany: From Lilienthal until Today:


  During the same year, the National Physical Laboratory (NPL) in Teddington/England started operating, for the first time ever, a supersonic wind tunnel based on the pressure storage principle ...