A motorcycle, at its most basic, is merely an object: two wheels, an engine, and a seat, on which a rider (if not a kickstand) keeps it all balanced. In America in the mid-20th century, the motorcycle was heavily laden with symbolism. It evolved into the must-have accessory for chaos agents—the James Deans and Evel Knievels of the world—and became an icon of the Hells Angels. But before that, motorcycles were largely practical machines, not symbols: Their spry bodies were used to deliver messages to and from the front lines in the First World War.