This is a military qualified GPS splitter with one-input and two outputs. It typically finds application where an input from an active GPS roof antenna is split evenly between two receiving GPS units. 

The MS12 can be configured to pass DC from an RF output (J2) to the antenna input port in order to power an active GPS antenna on that port. The remaining RF output would feature a 200 Ohm DC load to simulate an antenna DC current draw for any receiver connected to that port.