Originally, it was envisaged for use by nuclear submarines so that they could better aim their ballistic missiles. The system was so good that it soon found a long range of uses outside the military too as the DOD made a somewhat degraded version publicly available.

Since it became fully operational on April 27, 1995, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, scientific uses, tracking and surveillance, and hobbies such as geocaching and waymarking. Also, the precise time reference is used in many applications including the scientific study of earthquakes and as a time synchronization source for cellular network protocols.
China, Japan, India, and the European Union have initiated their own GPS programs. GPS receivers are now fairly inexpensive and have become ubiquitous. They are found on the bridge of almost every ocean-going ship in the world and are so relied upon that many mariners fear that traditional methods of position-finding, such as use of the sextant, will no longer be practiced.

Degraded signal and errors
While GPS is capable generally of identifying the position of the receiver within several meters, the accuracy may be degraded in a variety of manners. Because the radio signal transmitted by the satellite is weak, it is readily subject to interference. This interference may be generated by a number of sources.

Space weather, such as solar flares, may disrupt the signal. Metal in the vicinity of the receiving antenna may degrade the signal (this is a particular problem for portable GPS devices used in cars and on boats).

Man-made electro-magnetic interference (EMI) is a growing problem. In 2001, GPS reception in and around Moss Harbor, California was blocked. It took about a month to determine that this interference was caused by a defective television antenna on a recreational yacht docked at a local marina.