Those on the eastern side of the great Atlantic divide might like to consider the origins of the Instrument Landing System....never mind GPS.
A joint development by Sperry (an American company) and Reed Pigman...the latter individual was also greatly involved in the development of the VOR system of navigation.
Now, having said this, would I personally like to operate to CATIII with (augmented) GPS?
Ahhhh, no...not just yet.
NB.
Pigman also colaborated with Sperry on the development of the first 'true' flight director...the Sperry Zero Reader.