As a gifted Berkeley engineering graduate in the late teens, Hill succeeded in reengineering the famous "Liberty Engine" of World War I to fit into the legendary bomber DH-4, or "Flying Coffin." In the late 1920s his passion for aviation brought him to a new marketplace as twelve-year president of Air Associates - the remarkable catalog vendor of everything from plane parts and repairs to the whole aircraft.

During World War II, he founded his own company, manufacturing and distributing all the hose-clamps for the popular P-51 Mustang Fighter.

A true entrepreneur, Leroy Hill was involved in sixty different companies, either designing new technologies or marketing improved versions of the old. Politically, he was a lifelong anti-union activist working in the most unionized industries in the nation. Though he marched lockstep with no one, Hill remained to the end of his life a hardbitten opponent of big government who championed many conservative movements of his day.