The UK Ministry of Defence has contracted Imperial College London to build a quantum sensor that can track trains without relying on GPS, a technology that fails underground and remains vulnerable to jamming. The contract, signed in November 2025, is one piece of a broader push across British universities and startups to replace satellite-based positioning on railways with quantum inertial navigation. If the technology works at scale, it could reshape how rail operators locate trains in tunnels, dense urban corridors, and contested signal environments.
A Small Contract With Big Ambitions
The Quantum Inertial Navigation System project, known as Q-INS, is modest in scale but specific in purpose. According to the procurement notice, the Ministry of Defence awarded the contract to Imperial College of Science, Technology and Medicine on 7 November 2025, with a value of £62,500 excluding VAT. The contract runs through 30 September 2028, giving the research team nearly three years to develop and test a quantum inertial sensor designed for GPS-free positioning.
At £62,500, this is not a production deployment. It is a research-stage investment, the kind of seed funding that signals institutional interest without committing to full-scale rollout. The MoD’s involvement suggests that the military sees value in positioning technology that works when satellite signals are denied, whether by geography or interference. Rail is one of the clearest civilian testing grounds for that same problem: trains routinely pass through tunnels, cuttings, and station complexes where GPS drops out entirely. A sensor that can maintain an accurate position estimate in those environments would be equally valuable for defence logistics and for day-to-day passenger operations.
Imperial’s Sensor Already Rides the Tube
The Q-INS contract builds on work that has already moved from the lab to the tracks. In a recent update, Imperial College reported that its quantum sensor has been deployed on the London Underground and even taken to the Arctic for field trials of GPS-free navigation. The sensor uses quantum inertial sensing, measuring acceleration and rotation at the atomic level, to determine position without any external signal.
The core idea is to trap and cool atoms, then use their wave-like properties as exquisitely sensitive motion detectors. By integrating tiny changes in acceleration and rotation over time, the system can infer how far and in what direction a vehicle has moved. Unlike GPS receivers, which depend on signals from satellites, a quantum inertial sensor is self-contained. It keeps working in tunnels, under dense foliage, or in environments where radio signals are disrupted.
Joseph Cotter, the project lead at Imperial, has directed the development of this technology for environments where satellite navigation simply cannot reach. The Underground deployment is a meaningful proof of concept because it subjects the sensor to real-world conditions: vibration, electromagnetic noise from third-rail power systems, temperature swings, and the stop-start motion profiles of passenger trains. These are harsher test conditions than a controlled laboratory, and the fact that Imperial chose the Tube as a proving ground indicates confidence in the hardware’s readiness for rough environments.
The work also sits within a broader ecosystem at Imperial, where multiple research groups listed in the university’s staff directory are exploring quantum technologies for sensing, timing, and communications. That institutional base gives the MoD some assurance that expertise and equipment will still be available as the project evolves over several years.
MoniRail and the University Consortium
Imperial is not working alone. A separate but related effort is being led by MoniRail, a University of Birmingham spin-out that won Phase 2 funding from the DSIT and Innovate UK SBRI Quantum Catalyst Fund. In a university announcement, MoniRail’s project is described as developing a quantum-based navigation system for railways, with a particular focus on solving GNSS signal loss in tunnels.
The MoniRail project brings together a consortium that includes Transport for London, Imperial College, the University of Sussex, the University of Birmingham, and PA Consulting. The breadth of that partnership matters because it connects frontier physics research with an operator that runs one of the world’s most complex underground networks. TfL’s involvement means the technology is being shaped by operational requirements (such as integration with signalling systems, maintenance regimes, and safety certification), rather than by academic curiosity alone.
The Phase 2 award under the Quantum Catalyst Fund, detailed in the government’s competition overview, signals that MoniRail’s concept has cleared an initial feasibility hurdle. However, the latest publicly available information does not include post-award field test results. That leaves open questions about how the prototype performs over longer routes, in mixed-traffic environments, or under the full range of weather and loading conditions that a national rail network must handle.
Magnetic Mapping Offers a Parallel Path
While quantum inertial sensors measure motion to calculate position, a separate line of research suggests that the Earth’s magnetic field could serve as an independent positioning layer for trains. A research team has posted results on arXiv describing experiments that use spatially resolved magnetic field measurements matched against a pre-built magnetic map to locate trains on operational tracks. The experiments achieved track-selective, sub-5-metre accuracy over 21.6 kilometres of railway.
That level of precision is significant for rail operations. Knowing which specific track a train occupies, not just its approximate location along a route, is essential for safe signalling and for managing traffic on multi-track corridors. Traditional train detection systems, such as track circuits and axle counters, provide that information locally but do not offer a continuous, high-resolution position trace that operators can use for traffic optimisation or real-time diagnostics.
The magnetic approach and the quantum inertial approach solve different parts of the same problem. Inertial sensors track how a vehicle moves through space; magnetic maps confirm where it is relative to known infrastructure. A system that combines both could provide continuous, high-confidence positioning even in the deepest tunnels, without any satellite input at all. In practice, an operator might use inertial navigation to bridge gaps between magnetic landmarks, while the magnetic map periodically corrects any accumulated drift in the inertial solution.
Why GPS Alternatives Matter for Rail
Most coverage of GPS-free navigation focuses on military applications, where adversaries can jam or spoof satellite signals. But the civilian case for railways is just as pressing, if less dramatic. Every time a train enters a tunnel, its GPS fix disappears. For the London Underground, which operates largely below ground, satellite positioning has never been an option. For mainline railways, GPS blackouts in tunnels and urban canyons create gaps in real-time tracking that operators must fill with legacy systems like track circuits and balises, hardware embedded in the rails that is expensive to install and maintain and limited in the data it provides.
Quantum inertial navigation promises something different: a self-contained sensor that keeps tracking position regardless of what is happening to the signal environment outside the train. If the technology matures to production quality, it could reduce dependence on wayside infrastructure and give operators a continuous, high-resolution picture of where every train is at every moment. That has direct implications for capacity, because more accurate and timely position data allows signalling systems to run trains closer together while maintaining safety margins.
There are also resilience and security benefits. A rail network that relies heavily on GNSS is exposed not only to accidental outages but also to deliberate interference. Jamming devices are relatively cheap, and spoofing attacks have already been documented in other sectors. By contrast, an inertial or magnetic system cannot be jammed from a distance; an attacker would need physical access to the train or track, raising the bar for disruption.
None of this will happen overnight. The Q-INS contract is small, and the MoniRail consortium is still in a funded development phase. Both efforts must demonstrate that quantum sensors can survive years of vibration, shocks, and temperature cycles; that they can be maintained by railway technicians rather than quantum physicists; and that their cost can be justified against competing upgrades such as digital signalling or improved communications networks.
Yet the direction of travel is clear. With defence agencies commissioning targeted research, universities proving concepts on operational railways, and spin-outs building commercial systems, the UK is positioning itself to move beyond GPS for train localisation. If quantum inertial navigation and magnetic mapping deliver on their early promise, future passengers may never notice the change, but the trains carrying them could be navigating with atomic precision, entirely independent of the satellites overhead.
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*This article was researched with the help of AI, with human editors creating the final content.
