Another name I didn't recognize - I knew there was someone who did zone refining, and that it was critical, but didn't know the name. You likely already know of this, just not under this name; here: http://en.wikipedia.org/wiki/Double-Cross_System Briefly, during WWII, the British ran the entire German espionage system in the UK; initially, only for counter-intelligence purposes, but later on, to actively feed the Germans disinformation. For anyone who hasn't read it, I highly recommend R. V. Jones' book, "The Wizard War" - it covers all the various navigation systems (on both sides), and much more. I can also recommend "The Secret War", by Brian Johnson (the companion book to a BBC series), which covers that, radar, the V-weapons, code-breaking, and much more. Err... :-) Noel