From the earliest days of man's journeys he has depended on the basic signs of nature to guide him—the sun, the stars, and landmarks along the way. Technology developed over time, and man used new implements to better exploit these basic natural guides—the compass, charts, sextants, timepieces, and so forth. The last half-century has seen perhaps the greatest advances in navigation technology: precision radars, inertial navigation systems, computer-controlled aircraft systems, "paperless" charts, and the global positioning system. Unlike the natural guides they may exploit or replace, these technological wonders require an element that natural navigation aids do not—power and a permissive electromagnetic environment. Without this environment, these technological tools cannot function as they are intended.