How Militaries Navigate Without GPS, From INS to Quantum Sensors

Navigation without GPS has gone from Cold War afterthought to urgent priority, with civil aviation groups logging tens of thousands of GPS jamming and spoofing incidents a year around conflict zones since 2024. The fallback is a family of technologies led by inertial navigation, a sensor that needs no signal at all, plus terrain matching, celestial fixes and a new wave of quantum sensors.

0

External signals an inertial navigation system needs

~1 nmi/hr

Typical drift of a good aircraft-grade INS, roughly

3

Gyro families in service, ring laser, fiber optic, MEMS

1950s

Decade celestial-inertial navigation first flew on bombers

Why GPS fails in a war zone

GPS signals arrive at the receiver weaker than a light bulb seen from thousands of kilometers away, which makes them trivially easy to drown out. Cheap jammers blanket entire regions, and spoofers do something worse, they feed receivers plausible but false positions, a tactic now routine over the Baltic, the Black Sea and the Middle East. Ukraine has shown the operational cost, operators report that GPS-guided rounds such as GMLRS and JDAM saw their accuracy degrade sharply under Russian jamming until software and antenna fixes arrived. Militaries hardened GPS with encrypted M-code and controlled-pattern antennas, but the lesson stands, satellite navigation is a convenience that a peer enemy can take away, part of the broader electronic warfare duel.

An inertial navigation system answers the question “where am I” using nothing but physics. Accelerometers measure every change in velocity along three axes, gyroscopes track every rotation, and a computer integrates both from a known starting point, dead reckoning at thousands of updates a second. Because the INS neither transmits nor receives, it cannot be jammed, spoofed or detected.

The catch is drift. Tiny sensor errors accumulate, so position uncertainty grows with time, roughly a nautical mile per hour for a good aircraft-grade system and far better for the exquisite units in submarines and ICBMs. That is why almost every military INS is paired with something that resets the error, GPS when available, or the alternatives below when it is not. Weapons like Iskander and most cruise missiles fly on INS first, with everything else layered on top.

Ring laser vs fiber optic vs MEMS gyros

Gyroscope technologies compared

Technology	Accuracy class	Typical use
Ring laser gyro (RLG)	High; the airliner and fighter standard for decades	Combat aircraft, ships, missiles
Fiber optic gyro (FOG)	High, no moving parts, very reliable	Warships, submarines, guided weapons, land systems
MEMS gyro	Lower, but improving fast; chip-scale and cheap	Drones, artillery shells, small munitions
Hemispherical resonator gyro	Very high with tiny size and power draw	Spacecraft, high-end weapons
Mechanical/electrostatic gyro	Extreme accuracy, legacy	Ballistic missile and submarine navigators

Accuracy classes are broad generalizations; performance within each family spans orders of magnitude.

What can replace GPS

GPS alternatives and aids

Method	How it works	Limitation
Celestial navigation	Star trackers fix position against catalogued stars; used on bombers, SR-71 and ballistic missiles	Needs sky visibility; weather matters at low altitude
Terrain and scene matching	Radar or camera compares ground below to stored maps	Needs distinctive terrain and heavy mission planning
Magnetic anomaly navigation	Matches measured crustal magnetic field to survey maps	Maps incomplete; sensitive sensors required
eLoran and ground beacons	Powerful low-frequency terrestrial signals	Infrastructure must be built and can be targeted
Signals of opportunity	Uses TV, cell and satellite-internet signals as beacons	Depends on third-party transmitters
Visual odometry	Cameras track motion over ground, common on drones	Degrades at night, over water and in bad weather

Most fielded systems fuse several of these with an INS rather than relying on any single aid.

None of these is a drop-in GPS replacement, and that is the point. Modern “assured PNT” architectures fuse an INS with whichever aids survive the environment, star trackers above the weather, terrain matching for cruise missiles, magnetic and visual navigation for drones. Hypersonic weapons, which fly wrapped in plasma that blocks most signals, lean especially hard on inertial and celestial guidance.

The most promising long-term answer is quantum sensing. Cold-atom interferometers measure acceleration and rotation against the behavior of individual atoms, which do not drift the way mechanical or optical sensors do, and quantum magnetometers could make magnetic-map navigation far more precise. The UK, US, China and Australia have all flown laboratory demonstrators on aircraft, ships or trains in recent years. The systems remain bulky and sensitive, but the objective is explicit, an INS accurate enough that a submarine or bomber simply never needs an external fix.

Editor’s read

The GPS era trained a generation of planners to treat position as free information, and the last few years have been an expensive un-learning. The INS never went away, every serious weapon still carries one, and the money now flowing into quantum sensors, star trackers and terrain matching is really buying back what militaries had in 1975, autonomy, at modern accuracy. Expect “works without GPS” to become a standard line in weapons marketing.

How do military aircraft navigate without GPS?

Primarily with inertial navigation systems, backed by radio aids, terrain matching, star trackers on some platforms, and crew procedures that predate satellite navigation.

Can an inertial navigation system be jammed?

No. It measures the vehicle’s own motion and neither transmits nor receives, so there is nothing to jam or spoof. Its weakness is drift over time, not interference.

How accurate is an INS without GPS?

Roughly a nautical mile of drift per hour for a good aircraft system, much better for submarine and missile-grade units, and much worse for cheap MEMS sensors on small drones.

What is assured PNT?

Assured positioning, navigation and timing, the military term for architectures that fuse INS with multiple GPS-independent aids so navigation survives jamming.

Will quantum navigation replace GPS?

Not soon. Demonstrators have flown, but the sensors are still large and delicate. The realistic near-term goal is quantum-aided INS that drifts slowly enough to skip external fixes for days.

Sources