Hans Wolfgang Liepmann was an American engineer and emeritus Theodore von Kármán Professor of Aeronautics at the California Institute of Technology. He is known for his numerous contributions in fluid mechanics covering a wide range of problem areas, such as flow instability and turbulence, gas kinetics, viscous compressible fluids and liquid helium flows. He was born on July 3, 1914 in Berlin, Germany. Hans Liepmann received a Dr.Ing.h.c. from the University of Aachen and a Ph.D. from the University of Zurich in 1938. Liepmann was elected a member of the National Academy of Engineering and the National Academy of Sciences.  He was a recipient of the National Medal of Technology and the Ludwig Prandtl Ring—the highest honor conferred by the German Society for Aeronautics and Astronautics. In 1986, President Ronald Reagan awarded Liepmann the National Medal of Science. He died on June 24, 2009 in La Canada Flintridge, California, United States.