NavList:

Thanks Frank - I'm so sorry if I've caused a recurrence of nausea! 

Of course GNSS vulnerability is not a new problem but it hasn't yet been effectively addressed.

I am not an expert in this field but I have recently spoken to several people who are, and they are seriously concerned.  Even if jamming hasn't yet been seen to cause many problems, it is apparently very easy to knock out GNSS reception over a wide area.  The potentially disastrous consequences for many parts of our 'critical infrastructure' (not just navigation) of the loss of the GNSS time signature are causing particular anxiety.  This is why the US Administration is now planning to launch a form of eLORAN - see the letter of 8 December 2015 from the two co-chairs of the US National Executive Committee for Space-Based Position, Navigation and Timing (EXCOM) to Congressman Garamendi: http://rntfnd.org/wp-content/uploads/DSD-and-Dep-DOT-reply-to-Mr.-Garamendi.pdf.  

In answer to your question, eLORAN transmissions operate at far higher power levels than GNSS, on different frequencies, and are of course terrestrial.  So it's much harder to jam them.  

David