In 1963, in addition to examining the characteristics of the Omega system, we were also very concerned with a comprehensive navigation system study which was designed to examine all aspects of a world-wide navigation system operating in a B.O.A.C. type environment. This concerned a study of dead reckoning as well as externally referenced sources of information. You have the choice of an all dead reckoning system probably employing multiple sensors of the same type, triple IN is typical, or you could have a mixture of externally referenced and self-contained, in other words dead reckoning sensors. Occasional reference could be made to short-range aids or even a satellite system if available to increase the integrity of the position-fixing information. The inertial and computer aspects have been examined by the Avionics Department at R.A.E. whereas the radio sensors, which are externally referenced, and the relevant software have been the responsibility of the Radio Department.