GPS has become the navigation tool of choice...
The jamming of GPS is so trivial that any reasonably bright 14 year
old, can manage it - and within his allowance to boot..
Some older navcoms will jam the gps in the plane when tuned to certain
frequencies... A quick google search on the radio models and those
certain frequencies is enough information for one to build a wide area
gps jammer...

It used to be the gov't worried about a terrorist using the GPS to
guide a weapon to a precise point... Whereas, they should worry about
a terrorist blocking GPS over a wide area on a dark and stormy night,
with airliners unable to land, ships losing navigation near the coast,
etc...

denny