Abstract: A system for, and method of, blending (or integrating) pseudo-range or position measurements and bearing-to-transmitter measurements from an eLORAN or LORAN-C receiver and position (alternatively, pseudo ranges) and velocity (alternatively pseudo-range rate) measurements from a GPS receiver. The described system can also be integrated with additional external positioning systems. In the context of an inertial navigation system (INS) application, this combined GPS/LORAN signal can be employed to provide external positioning solutions, potentially integrated with measurements from devises such as accelerometers, gyroscopes, altimeters, etc. The system includes a GPS signal input, a LORAN signal input, preprocessors for each, and an integrator to combine the two preprocessed signals to estimate errors in the full trajectory variables.