In 2015, the US Naval Academy put celestial navigation back in the syllabus after dropping it in 1998; officers learn the sextant in case GPS is jammed or spoofed

Most modern navigation relies on GPS: a receiver reads a satellite signal and returns a location on a screen. That system has been reliable for the US for decades. The US Navy is preparing for the possibility that it won't always be. According to a 2015 Military Times report, the US Naval Academy reinstated celestial navigation in its training curriculum in 2015, seventeen years after the practice was quietly abandoned. The reason? Not some sort of love for the tradition, but because they feared that the satellite grid we all operate within could somehow be rendered useless, and an entire generation of officers had no idea what to do about it.

A skill used by sailors since 1845, gone in a decade

Celestial navigation, which comprises taking angles of stars, the sun, or moon against the horizon to determine one's current position, was a part of US Naval Academy training since the school's founding. In 1998, computers rendered that training largely useless, and the full program was quietly scrapped. It wasn't only Annapolis, either; celestial navigation eventually faded out of all parts of the US Navy's training.

This fear wasn't unwarranted. After all, GPS is cheap, precise, and convenient. It's easy to assume that if the technology fails, there's little use in having it in the first place. Except that, as a US Naval Academy navigation instructor lamented shortly before the practice ended, "it leaves us with no backup" if the GPS does fail.

The backup nobody built

That assessment wasn't made first in 2015, when the practice was reinstated. A 2001 vulnerability assessment produced by the US Department of Transportation's Volpe National Transportation Systems Center, undertaken at the direction of a 1998 presidential decision directive (PDD-63) and publicly released on September 10, 2001, the day before the September 11 attacks, had already found that GPS-reliant systems were vulnerable to spoofing, interference, and outright attack. The report highlighted the ways in which GPS had been made ubiquitous, including in aviation, shipping, finance, and telecommunications timestamps, but those vulnerabilities remained woefully understudied and unmitigated. Spoofing GPS receivers allows an attacker to give false information to any system that trusts the receiver's location data. While jamming receivers can drown out GPS satellites' signals (which most receivers will note and respond to), spoofing is far more insidious because it can send false location data to a receiver without signalling anything is wrong.

According to a 2008 paper titled “Assessing the Spoofing Threat: Development of a Portable GPS Civilian Spoofer,” written by engineer Todd Humphreys and his colleagues, and published via the Institute of Navigation, the researchers built a portable device capable of spoofing civilian GPS receivers to demonstrate just how feasible such an attack would be. Five years later, in 2013, Humphreys and a University of Texas team put that line of research to a real-world test: they successfully spoofed the GPS receiver aboard an $80-million superyacht in the Mediterranean, tricking it into believing it was somewhere it wasn't while its crew watched instruments that showed nothing wrong.

This isn't a Cold War hypothetical anymore

The Baltic Sea has become a testing ground for exactly this kind of threat. So far this year alone, tens of thousands of commercial aircraft have had their GPS receivers interfered with, and a few particular flights saw their aircraft tricked into "circling a point on the globe" that they didn't actually pass over. The UN's aviation, maritime and telecom agencies jointly released a statement of "grave concern" about this kind of interference, which has been happening with increasing frequency since late 2023.

Why should any of this matter

Reliance on GPS for everyday navigation is now nearly universal, and that convenience comes with a cost the Navy is trying to hedge against. The Navy isn't reviving celestial navigation out of nostalgia; it's responding to exactly the vulnerabilities the spoofing demonstrations, the 2001 report, and the Baltic Sea incidents have all pointed to. Annapolis midshipmen only get a few hours of celestial-navigation theory, which likely isn't enough on its own to build real proficiency with a sextant: the same limited scope that made the training seem dispensable back in 1998. But a partial, imperfect backup is still what the Navy has chosen over none at all, on the reasoning that some ability to navigate without satellites is better than a fleet that has none if the satellites ever go dark.