pointed out by John Freeman is this site The Decca Legacy
From the Reg Simmonds archive, great reading to understand where we were in the 1950s on forthcoming navigation systems, especially if you have an interest in DECCA and DECTRA. There are two maps in Appendix C that are too big for us to scan so they are reproduce below by other means. Hopefully better versions will follow.
following on, from Barry Davison is a brochure on a Eurocontrol proposal for a Radio Area Navigation System (HARCO) for Europe.
now we have a brochure on DECCA and DECTRA. One map has proved impossible to reproduce in the brochure so the map is displayed separately.