Since GPS achieved Fully Operational Capability on July 17, 1995, GPS has become an essential navigational tool for civilians and military alike. Keeping the system up-to-date has proved to be a problem. Originally the system was supposed to be up and running in February of 2016 but has been delayed at least until 2023.
The latest iteration of the GPS satellite array is called GPS Block III. These satellites must be launched (and will greatly increase navigational accuracy) in order to keep the Navstar global positioning system operational.
The satellites have already been built by Lockheed-Martin and consist of ten new, advanced satellites to be launched into orbit by SpaceX Falcon rockets. The hold up is the U.S. government wanting to make sure the hardware actually gets up there as they independently seek to confirm the safety and reliability of the SpaceX rocket systems.
The new GPS satellites will boost additional easier to track signals for civilian navigational uses and a Military code (M-1) providing anti-jamming security use for the military.