Nation: The Spy Planes: What They Do and Why

THE pilots of Sopwith Tabloids, French Nieuports and German Taubes opened the age of aerial combat by taking potshots at one another with rifles in the skies of World War I Europe. But the first military function of aircraft in that war was gathering intelligence. Tiny, unarmed biplanes scurried behind enemy lines to spy out troop dispositions and act as airborne forward artillery observers. Warfare has grown immensely more complex in the half-century since then, but gathering intelligence nonetheless remains one of the airplane's most significant and fascinating functions.

Present-day spy planes, with...