How did researchers go about investigating trans-sonic flight?

The Research Airplane Program was a joint research effort by the National Aeronautics and Space Administration (NASA-formerly the National Advisory Committee for Aeronautics or NACA) and the military services. It was conceived near the end of World War II to perform flight studies with a series of specially-constructed research aircraft in the then-unexplored transonic to low-supersonic characteristics of full-scale aircraft in flight.

Ithink it’s cancer risk