 In 1940, Kearny went on active duty as an infantry reserve lieutenant in the United States Army.Recognized for his knowledge of jungle travel and use of specialized tools and equipment, Kearny was soon assigned to Panama as the Jungle Experiments Officer of the Panama Mobile Force, and was promoted to captain.In that capacity he was able to invent, improve, and/or field test much of the specialized jungle equipment and rations used by U.S. infantrymen in World War II.