The Loran C system discontinued from 31 Dec 2015

[Jens Heri]

The Loran C stations in Norway, Faroe Islands and France stopped transmission from midday Dec. 31 2015. The Faroese station has transmitted its Loran C signal since the 60ies.

 http://www.nrk.no/nordland/_-dette-systemet-kan-hindre-en-nasjonal-krise-av-uante-dimensjoner-1.12728059

[Captain Ted]

:-(
there goes another part of shipping history

[Bob Scott]

So if GPS were ever to go down, it would be back to the sextant, I suppose!

[davidships]

Much will depend on on how the European-funded Galileo system is accepted - it is due to start to come on stream later this year (at present 12 of the 24 operational satellites are in place and full operational status will be reached in 2019.  The free-to-use signals are intended to give an accuracy of 1 metre (1cm for specialist paid services) - GPS is, I think, 15 metres, though that can be reduced to 3-5m in coastal areas with Differential GPS (by using, for example, a fixed radio beacon).  That it, I suppose, sufficiant for normal navigation.

[Jens Heri]

GPS satellites can be knocked out by a powerful sun storm.
GPS signals can be jammed - South Korea has experienced it at times.