Global Positioning System

The Global Positioning System (GPS), originally developed for U.S. military applications, is the most widely used part of the Global Navigation Satellite System. It provides both precision position and time information.

A "selective availability" mode can be invoked for specific areas, in which the high-precision information will be available to receivers only with military cryptographic keys, but the general trend to assume that it is more useful to have accurate signals available than selective ones. By not going into SA mode, commercial equipment can quickly be adapted to military use, as was done with handheld navigation receivers in the Gulf War. Civilian ships and aircraft also depend on accurate signals.