While the ideas behind it were developed much earlier, GPS didn't become fully operational until 1995 [1].
It's also worth noting, on the other hand, that the (not yet fully operational) system was used during the first Gulf War. [2]
[1] http://tycho.usno.navy.mil/gpsinfo.htmlThe U.S. Air Force Space Command (AFSC) formally declared the GPS satellite constellation as having met the requirement for Full Operational Capability (FOC) as of April 27, 1995.
It's also worth noting, on the other hand, that the (not yet fully operational) system was used during the first Gulf War. [2]
[1] http://tycho.usno.navy.mil/gpsinfo.html The U.S. Air Force Space Command (AFSC) formally declared the GPS satellite constellation as having met the requirement for Full Operational Capability (FOC) as of April 27, 1995.
[2] http://www.gpsnavigatormagazine.com/gps-at-war.html