Both military and civilian uses are available
The primary military purposes are to allow improved command and control of forces through improved locational awarness, and to facilitate accurate targeting of smart bombs, cruise missiles, or other munitions. The satellites also carry nuclear detonation detectors, which form a major portion of the United States Nuclear Detonation Detection System.
The system is used by countless civilians as well, who can use the GPS's Standard Positioning Service worldwide free of charge. Low cost GPS receivers (price $100 to $200) are widely available, combined in a bundle with a PDA or car computer.
The system is used as a navigation aid in aeroplanes, ships and cars. The system can be used by computer controlled harvesters, mine trucks and other vehicles.
Hand held devices are used by mountain climbers and hikers. Glider pilots use the logged signal to verify their arrival at turnpoints in competitions.
Military (and selected civilian) users still enjoy some technical advantages which can give faster satellite lock and increased accuracy.
The increased accuracy comes mostly from being able to use both the L1 and L2 frequencies and thus better compensate for the varying signal delay in the ionosphere.
Commercial GPS receivers are also required to have limits on the velocities and altitudes at which they will report fix coordinates; this is to prevent them from being used to create improvised cruise or ballistic missiles.
GPS can be jammed
A large part of modern munitions, the so-called "smart bombs" or precision-guided munitions, use GPS. GPS jammers are available, from Russia, and are about the size of a cigarette box.
The U.S. government believes that such jammers were used occasionally during the U.S. invasion of Afghanistan.
Some officials believe that jammers could be used to attract the precision-guided munitions towards noncombatant infrastructure, other officials believe that the jammers are completely ineffective. In either case, the jammers are attractive targets for anti-radiation missiles.
Related topics about "technology":
Geographic Information System (GIS): Index;
Global Navigation Satellite System (GLONASS);
Global Positioning System (GPS);