Being able to locate yourself anywhere in the world isn't half as important as your need for instant communication. Cellular networks are one more thing you can thank the military for. In 1985 the US Army started researching a technology called Mobile Subscriber Equipment, which forms the basis of modern cellular technology.
MSE used signal towers deployed on the backs of Humvees to deliver service to mobile units mounted on other trucks. The signal towers acted just like modern cell towers, allowing forward operating soldiers to have communication as long as they were in network. Signal would jump from tower to tower, just like the modern cellphone.
The tech was first tested in Desert Storm in early 1991, and has since evolved into the always-on networks we use today.
Image: US Army Signal Corps