Progress in gas dynamics coincides with the developments of transonic and supersonic flights.  As aircraft began to travel faster, the density of air began to change, considerably increasing the air resistance as the air speed approached the speed of sound.  The phenomenon was later identified in wind tunnel experiments as an effect caused by the formation of shock waves around the aircraft.  Major advances were made to describe the behavior during and after World War II, and the new understandings on compressible and high speed flows became theories of gas dynamics.
As the construct that gases are small particles in Brownian motion became widely accepted and numerous quantitative studies verifying that the macroscopic properties of gases, such as temperature, pressure and density, are the results of collisions of moving particles, the study of kinetic theory of gases became increasingly an integrated part of gas dynamics.  Modern books and classes on gas dynamics often began with an introduction to kinetic theory.  The advent of the molecular modeling in computer simulation further made kinetic theory a highly relevant subject in today's research on gas dynamics.