Abstract: A VLF navigation system suitable for highly accurate worldwide aircraft navigation utilizing existing VLF transmitting stations on a "dead reckoning" basis with initial and intermediate fixes. The system is enabled to utilize all existing VLF transmitting stations regardless of station frequency by novel receiver phase-locked loop means which normalizes all station frequencies to phase coherent independent data signals of a common working frequency. In one form of the invention, utilizing hyperbolic coordinates, both RF stations of each station pair utilized for computation are such VLF transmitting stations; while in another form of the invention, utilizing Rho-Rho coordinates, one RF station of each station pair is an on-board frequency standard normalized to the common working frequency, and the other station of each pair is one of the VLF transmitting stations.