What do you do when your ship and crew ends up in a conflict zone with no reliable position?

When GNSS and AIS signals become unreliable in a high-tension region, the immediate priority is to retain safe navigational control of the vessel, according to Steffen Grefsgård and Rob Gillette

The bridge team must quickly determine whether they are experiencing signal degradation, deliberate jamming or active spoofing. Autopilot settings may need to be disengaged. Positions must be cross-checked using radar, visual bearings and any available independent references. Shore management and insurers may need to be notified. Most critically, the crew must establish whether the vessel’s reported position can still be trusted.

Interference incidents have been documented repeatedly in the region over the past year. However, the present conflict – including the effective closure of the Strait of Hormuz – has left hundreds of vessels stranded in the Gulf and intensified the operational risk environment.

Electronic interference becomes operational reality

Since mid-2025, the maritime industry has documented repeated episodes of AIS and GNSS disruption in the region. In recent days, these incidents have coincided with direct attacks on tankers and formal warnings advising operators to expect jamming and spoofing during ongoing military activity.

Hundreds – sometimes thousands – of vessels have appeared in incorrect locations, in some cases plotted inland or at airports. The consequences include rerouting, port suspensions and sharp increases in war-risk insurance premiums.

But the problem extends far beyond the Gulf. Electronic interference is already widespread across global shipping routes. A recent survey by the Royal Institute of Navigation (RIN) found that 79% of maritime respondents had personally experienced GNSS interference, highlighting how disruption has moved from isolated incidents to a normalised operating condition across several maritime regions.

What breaks when GNSS cannot be trusted

Modern ships rely on Positioning, Navigation and Timing (PNT) data – typically derived from GNSS such as GPS. On many vessels, GNSS has effectively become the positional and timing reference spine for multiple bridge and safety systems.

ECDIS, AIS transmissions, GMDSS, radar overlays and autopilot functions all depend on this reference.

However, when GNSS integrity is compromised:

• Navigation accuracy deteriorates. ECDIS positioning may drift; autopilot reliance becomes unsafe.
• Situational awareness degrades. Port authorities, Vessel Traffic Services (VTS) centres and shore security teams receive false AIS tracks. Rendezvous and pilotage become complicated.
• Compliance exposure increases. Manipulated AIS data can create the appearance of sanctions breaches or unauthorised port calls.
• Insurance and commercial risk escalate. War-risk premiums rise, P&I clubs issue advisories and disputes may arise over deviation, delay or cargo claims.

In short, when GNSS fails, the vessel loses its single point of positional truth.

The operational response requires an independent reference.

Independent PNT in a GNSS-denied environment

Utilizing an alternative source of PNT, independent of GNSS, is a key recommendation from the Royal Institute of Navigation. This approach for providing resilient PNT refers to leveraging an alternative source of position data that does not rely on conventional GNSS signals.

In contested or electronically congested waters, an independent PNT capability allows a vessel to verify its true location even if GPS or other satellite constellations are jammed or spoofed.

PntGuard has been developed specifically to provide that independent assurance for maritime operations. The system operates as a standalone layer, separate from existing bridge electronics. It comprises:

• An above-deck receiver connected to Iridium’s low-Earth orbit satellite signal
• A dedicated bridge display installed below deck (below-deck unit)

Because it functions independently of the vessel’s primary GNSS feed, it remains unaffected when GNSS signals are manipulated.

How independent PNT maintains navigational control

In high-risk waterways, several capabilities become particularly relevant:

1. Verified coordinates independent of GNSS

PntGuard utilises a secure APNT signal approximately 1,000 times stronger than conventional GNSS transmissions. If GPS signals are jammed, spoofed or time-shifted, the vessel retains access to authenticated coordinates that cannot be falsified through satellite interference.

This maintains navigational continuity when primary systems are compromised.

2. Real-time interference visibility

On the dedicated bridge display, officers can see how jamming or spoofing is affecting GNSS inputs. Signal degradation and discrepancies between GNSS and assured coordinates are visible in real time, supporting safe operation of ECDIS, AIS, GMDSS and autopilot systems.

3. Continuous onboard voyage recording

The system records verified vessel positions throughout the voyage, creating a secure track history. In contested waters, this becomes a commercial and legal safeguard – supporting post-incident reconstruction, sanctions verification and defence against false AIS track allegations.

4. Independent reporting to insurers

During interference events, verified position reports can be transmitted directly to war-risk insurers. This provides underwriters with independent maritime situational awareness, reducing ambiguity in claims handling and strengthening transparency between owner and insurer.

5. Assured coordinates during SAR

In a Search and Rescue (SAR) scenario where GNSS data is unreliable, verified coordinates can be transmitted to rescue authorities, reducing the risk of response assets being directed to incorrect locations.

Proven resilience

The underlying APNT technology has been in use for more than a decade across multiple industries, including government and defence, with more than 10,000 units deployed in GNSS-denied environments.

For maritime use, PntGuard has accumulated more than 100,000 nautical miles of commercial sea time and has been validated through government-supported trials and real-world operational environments including the Middle East, Ukraine and the Baltics.

From redundancy to strategic safeguard

Electronic interference is becoming a recurring operational challenge in strategic chokepoints – and increasingly in European waters.

In such environments, independent PNT capability is no longer simply a technical redundancy. It is becoming a strategic risk-control measure.

When a vessel enters a region with unreliable positioning, the priorities are clear:

• Establish a trusted reference
• Maintain navigational continuity
• Preserve defensible records
• Protect crew, cargo and compliance posture

As GNSS disruption spreads and ship systems grow more dependent on satellite positioning, independent PNT is rapidly becoming essential for safe and resilient operations.

Steffen Grefsgård is CEO of SGM Technology, and Rob Gillette is Assured PNT (APNT) Director at NAL Technologies.