How can ANYBODY but the USA build cruise missiles that use GPS?
Think about it. You are North Korea and build cruise missiles using GPS to attack South Korea, Japan or the USA. You launch your cruise missile barrage. The launch is detected by USA spy satellite. The USA now knows about the attack. The USA then SHUTS DOWN GPS, or ALTERS the coding of position-time information. Now your missiles ALL go off course. Not a very good idea.
Inertial guidance can not be jammed or diverted.
David F Mayer