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This article is part of the Fortune series, “When GPS goes wrong.”

The Global Positioning System has transformed everyday life over the past two decades. But the revolutionary system was far longer in the making.

Like many other pieces of world-changing technology, GPS can trace its genesis to the battles and the arms races of World War II. But far from bursting onto the global stage, the system—which uses satellites positioned around the globe to provide accurate timing and location to tens of millions of travelers and countless businesses—endured a long and fraught gestation period, deep within the U.S. military bureaucracy, largely out of sight.

And if the advent of GPS included several unexpected twists and turns, the scale of its eventual impact has also proved surprising. Today, it’s not just helping us get from A to B, but often shifting how we look at time and space entirely.

in 1983 then-President Ronald Reagan suggested that GPS should be used in the civilian realm as a navigational safety net.

Bad kids

During World War II, militaries needed a radio navigation system—and all had their own benefits and drawbacks. Some were good for guiding blind bombing missions, others for traversing the English Channel in bad weather, or hunting U-boats.

In the U.S., the different needs of different users meant a fragmented system, where several branches of the military used different technology. In the years after the war, many experts in the Department of Defense acted under the assumption that this system would gradually simplify.

That didn’t happen, explains William Rankin, a professor of the history of science at Yale and author of After the Map: Cartography, Navigation, and the Transformation of Territory in the Twentieth Century. Instead, the military systems remained staunch rivals, each jealously guarded, even as the U.S. entered the Sputnik era and began launching the satellites into space that would eventually make GPS possible. Eventually, the Department of Defence attempted to create an entirely new system, by instituting a “top-down program of getting these bad kids to play with each other,” as Rankin puts it, that resulted in modern GPS finally taking shape in 1973.

It was officially created as the first project of a Department of Defense project called the Joint Program Office. The new GPS program combined elements of two systems already under development, one under the Air Force and the other under the Navy. But the system for years remained deeply unpopular among some branches of the military. “Everyone hates [it],” says Rankin, recalling that era. “It doesn’t have wide support for its first decade at all.”

In 1983, the tide began to shift. That year, an error with the plane’s internal navigation systems resulted in a Korean Airlines jet being downed over Soviet airspace, causing a crash that killed everyone on board including a U.S. Congressman. After the accident, then-President Ronald Reagan publicly committed to creating a GPS system used by both the military and civilians, as a navigational safety net. In the early 1990s, the system gained credibility after it played a fledgling role in the first Persian Gulf War. By the mid-1990s, it was finally being used commercially, including in industries like shipping, for more accurate navigation.

By the 1960s the U.S. was instituting a “top-down program of getting these bad kids to play with each other,” as William Rankin, an associate professor of the history of science at Yale and author of “After the Map: Cartography, Navigation, and the Transformation of Territory in the Twenty-First Century” says. Instead, the military systems remained staunch rivals, each jealously guarded.

But the real jump to GPS becoming ubiquitous came in the 2000s. In 2000, then-President Bill Clinton announced that the military would stop intentionally degrading the quality of the “civilian” GPS signal, allowing the system to become far more robust and accurate. And over the ensuing years, GPS receivers became smaller and smaller, allowing them to make their way into all kinds of portable products—including smartphones. By the mid-2000s, “it’s in everything,” says Rankin.

Never lost

What the early creators of GPS couldn’t have anticipated is not just the sheer number of applications that would be found for the system, but the way it would change how we move through the world at large. For many of us, traveling anywhere now involves perceiving our place in space as a tiny, roving blue dot on a confined screen.

Now, “there is this sense that time and space are just fundamentally known quantities, and there really aren’t places in the world where can’t not know where you are, as long as you have the right receiver,” says Rankin. That’s an idea that even 30 years ago would have been “baffling,” he points out.

Rankin himself rejects the idea that GPS, in its efficiency and convenience, has wreaked havoc on our ability to rely on our own senses—after all, in the GPS age, we’ve gained new skills that allow us to navigate. But he does note that where everyday people used to look to multiple sources of information to know our place and time in the world, we now rely disproportionately on the one.

“That does make it more fragile, and all of your eggs are in one basket,” he says.

To merely focus on how GPS makes it easier to navigate is to miss what’s really transformative about the system. Because of its ability to offer highly precise timing, it also allows vast networks—cellphone towers, banking systems, and electrical grids—to synchronize, creating the kind of seamless communication we now take for granted.

That ubiquity extends into places that you may not associate with GPS, and applications that it was probably never anticipated it would be used for—not just the high-stakes ones involving financial networks and missiles, but examples that affect us in a profoundly ordinary way. One example Rankin’s finds fascinating: the timing of ordinary traffic lights.

“Not timing of a nuclear warhead [or a] stock trade kind of thing. Just stop lights.”