This object is a GPS receiver made by Navstar Systems from 1993. The unit builds on from the XR3 GPS system. This receiver is designed to plug into wider systems that provide the displays and mapping or provide data back to a central server over communications links, hence it has no displays or buttons.
It is encased in a rugged military spec enclosure and connectors. The receiver could also be used as a GPS Measurement sensor to provide input into more sophisticated external positioning software.