If you are interested in the history ofNavigation tecniques and equipment in general there are a few books i can recommend.
http://www.woodfieldpublishing.co.uk...n-uk/p177.html
http://www.amazon.co.uk/Quest-All-we.../dp/1840372591
I have both, and they have really helped me understand navigation in ww2. also from time to time on e-bay you can get RAF navigation manual 1941 or 1944, i have the 1944 version picked it up (original copy, hardback) for about £10.00, its very comprehensive, although does not go into radio navigation much.
regards
slipper
p.s almost forgot some free downloads here for radio nav systems in ww2
http://www.radarworld.org/books.html