INTUITION
Trying to figure out where you are and where you're going is probably one of man's oldest endeavors. Navigation and positioning are crucial to so many activities and yet the process has always been quite cumbersome. Over the years many technologies have tried to simplify the task but every one has had some disadvantage.
Finally, the U.S. Department of Defense decided that the military had to have a super precise form of worldwide positioning. And fortunately they had the kind of money ($12 billion!) it took to build something really good.
But you could only expect to hit a silo if you knew exactly where you were launching from. That's not hard if your missiles are on land, as most of them were in the Soviet Union. But most of the U.S. nuclear arsenal was at sea on subs. To maintain the balance of power the U.S. had to come up with a way to allow those subs to surface and fix their exact position in a matter of minutes anywhere in the world
Hello GPS !