The jamming of radio signals is almost as old as radio itself. In 1899, a rival newspaper attempted to jam the New York Herald's ship-to-shore reporting of the America's Cup race results. Ever since, jamming has been used by governments, military forces, and others to deliberately interfere with radio communications to prevent their successful reception. Its use was perhaps most prevalent during the Cold War when shortwave broadcasts from the West were regularly jammed by Warsaw Pact countries.
During military operations, jamming of an adversary's radio and radar signals is a common tactic and, in fact, is now an integral part of electronic warfare. In an attempt to thwart such jamming threats, military planners are continually developing antijamming techniques. Such is the case with GPS. Although its spread-spectrum nature affords it some protection from interfering signals, the signal is so weak that it can be readily overpowered by even a low-power nearby jammer or by a strong jammer at distances of up to many hundreds of kilometers.