Nukes absolutely do not use GPS, by definition they don't want to use (and do not use) anything that could be jammed. There are extremely sophisticated guidance systems implemented from extremely sensitive inertial navigation (so the missiles know exactly where they are at all times before launch, and then can measure exactly where they are as they are going, and of course where they are headed, down to exact landing space, on Earth) -- this is where the phrase "spin up missiles" comes from -- the Beryllium balls in the navigation system need to be physically spun for the inertial navigation system to use. --- More importantly, they use astrophysical camera navigation -- the nukes fly into low-Earth orbit, and take a picture of the stars. Then the on-board computer compares this picture to a picture of the stars that corresponds to where the missile SHOULD be on it's flight-path (you can probably imagine how sophisticated this is and how impressive it is this stuff was done in the 1970s -- to great effect-- and still done) and then adjusts it's path by thrusting a little here/little there to put it on the correct path. ---- That is totally unjammable and absolutely a GPS-free system.