The Political Path to GPS: How war and peace forged the universal map
thenewatlantis.com
thenewatlantis.com
"President Reagan announced on September 16, 1983, that the Global Positioning System (GPS) would be made available for civilian use, free of charge, once completed in order to avert similar navigational errors in the future."
[0] https://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_007
https://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_007
It was one of the biggest reasons why the military-only GPS system eventually became available for civilian use.
I’m not sure just what they do, but there are several possibilities for a submerged launch to use GPS. The sub could surface periodically to take GPS readings and keep the fix up to date with other systems, or it could run an antenna up to the surface, or it could let the missiles acquire their own fix after they breach the surface.
Keep in mind that high accuracy is mostly important for a first strike, when you’re trying to destroy the enemy’s nuclear weapons in hardened targets. A second strike can be much less accurate and still be useful. So the idea that you can’t use GPS because it will be destroyed in the war doesn’t necessarily apply.