GNSS Resilience on Ships: Jamming and Spoofing Response Plan for Ship Operators
February 24, 2026
GNSS disruption is no longer a rare edge case, it is an operating condition that crews are being warned to expect in certain regions, with jamming and spoofing risks explicitly raised by UN agencies and reinforced by practical guidance aimed at ship operators. The operational goal is not to “detect interference” in the abstract, it is to keep safe navigation when position trust drops, and to produce a proof-grade record that stands up in internal review, insurer questions, and any later investigation.
Detection and confirmation, what crews can trust in the moment
Goal: avoid false certainty, cross-check fast, then switch to a safer navigation posture when position trust drops
Working rule: treat GNSS as a sensor, not a truth source. If indications conflict, downgrade confidence, increase cross-check frequency, and log the evidence chain (time window, symptoms, cross-check results).
| # | Indicator you can observe | Onboard | Fast cross-checks that help confirm | Immediate posture shift | Tags |
|---|---|---|---|---|---|
| 1 |
Position jump that violates physics
Sudden move that implies impossible speed or track change.
|
ECDIS track leaps, sudden COG or SOG changes that do not match the ship’s feel, or a position that appears inland or offset from the visual scene. | Compare with radar ranges and bearings to fixed targets, compare DR track to GNSS, compare multiple GNSS receivers if available, verify gyro and log consistency. | Increase manual cross-check cadence, treat position as low confidence, slow down if needed to regain margin. | High risk |
| 2 |
Track looks “too clean” while the scene does not
A smooth plot that conflicts with radar, visual, or expected set and drift.
|
GNSS position appears stable, but radar and visual cues suggest different relative motion, or the vessel is not where you expect relative to aids to navigation. | Radar overlay sanity check, bearings to conspicuous objects, compare with paper or alternative plotted fixes, check echo sounder consistency with charted depths where applicable. | Treat as possible spoof, shift to conservative navigation, prioritize radar and visual fixing. | Spoof |
| 3 |
Loss of GNSS or degraded accuracy alarms
Receiver flags poor geometry, no fix, or integrity warnings.
|
GNSS alarm cascade, accuracy or integrity warnings, intermittent fix, or frequent loss of satellites. | Confirm receiver status pages, compare to other receivers, check time sync behavior, verify that other RF sources are not interfering onboard. | Treat as likely jamming or degraded environment, expand margins, slow or hold if approaching hazards. | Jam |
| 4 |
AIS position inconsistent or “teleporting”
AIS is open VHF and can be spoofed.
|
Own ship AIS or targets show positions that do not match radar or visual contact, or targets appear to jump or duplicate. | Use radar as primary target truth, compare AIS against radar plots, check for duplicate MMSI or abnormal static data changes, confirm with VHF where appropriate. | Do not use AIS alone for collision avoidance or safety decisions, treat AIS as advisory only. | AIS |
| 5 |
Multiple systems disagree about time or position
Integrated bridge systems can cascade bad time or position.
|
ECDIS, conning, DP, and automation layers show mismatched positions, timestamps, or alarms that do not reconcile. | Identify the time source, isolate which sensor is feeding the bus, compare independent sources, use manual fixes and radar to anchor the truth. | Reduce reliance on integrated overlays, isolate questionable inputs, increase bridge team focus and lookout. | Systems |
| 6 |
Regional pattern, other vessels report issues
Interference can be geographic and persistent.
|
Multiple vessels in the area experience similar GNSS anomalies or AIS weirdness, often reported via industry advisories and operator networks. | Check internal fleet advisories, bridge team reports, and company security bulletins, document the timeframe and location for later reporting. | Treat the zone as degraded GNSS, adopt conservative navigation and reporting posture until clear. | Pattern |
GNSS Degradation Triage
Fast, crew-friendly way to convert observations into a confidence tier and immediate actions
Pick the closest observations. Output is a directional confidence tier and a short action set to reduce risk while you confirm.
Position confidence tier
Caution
Directional, based on inputs
Likely interference type
Unknown
Not a verdict, a working hypothesis
Immediate action emphasis
Cross-check
What to prioritize in the next minutes
Directional decision aid only. Bridge team and master remain responsible for safe navigation, watchkeeping, and any maneuvering decisions.
Once the bridge team decides GNSS trust is degraded, the priority shifts from “diagnosis” to controlled execution: widen margins, tighten fix discipline, use independent sensors as the primary truth, and make sure every key choice is logged in a way that can be reviewed later. That approach aligns with recent operator guidance and official warnings, which emphasize practical steps, cross-checking, and disciplined reporting when interference is suspected.
Response actions, keep it safe first, then make the record defensible
Use case-based actions that crews can execute fast, especially near hazards or during pilotage and restricted visibility
Operator goal: maintain safe navigation under degraded PNT, reduce dependence on GNSS, increase independent fixing, and document the evidence chain (time, symptoms, cross-check outcomes, actions taken).
| # | Operating scenario | Immediate actions that reduce risk | Fast fixing and cross-check cadence | Record that holds up later | Tags |
|---|---|---|---|---|---|
| 1 |
Open ocean, wide margins
Use the space to stabilize the situation.
|
Treat GNSS as low confidence if symptoms persist, reduce reliance on GNSS-based overlays, increase radar and visual cross-checks, consider speed reduction if uncertainty grows. | Use DR as a backbone, validate with radar ranges and bearings where possible, compare multiple receivers if available, document any recurring pattern or zone behavior. | Start and end times, symptom type, screenshots of alerts, DR vs GNSS differences, any course or speed changes taken to regain margin. | Stabilize |
| 2 |
Coastal, traffic lanes
Assume the risk grows faster than the paperwork.
|
Increase lookout and bridge team focus, prioritize radar plotting, consider speed reduction, widen CPA margins, avoid relying on AIS for collision avoidance. | Radar ranges and bearings to fixed objects, frequent position sanity checks against expected set and drift, compare ECDIS radar overlay alignment, manual fixes as available. | Time-stamped fixes and cross-check notes, traffic situation summary, any near-miss avoidance actions and communications. | Collision risk |
| 3 |
Approach, pilotage, confined waters
This is where false certainty causes groundings.
|
Treat GNSS degradation as a trigger for conservative navigation posture, consider delaying pilotage evolution if margins are low, ensure pilot-master exchange includes degraded GNSS conditions. | Radar as primary truth, frequent range and bearing fixes, echo sounder consistency checks where meaningful, clearly identified DR track, explicit confirmation of reference sensors. | Who declared GNSS degraded, what cross-checks failed, pilot-master discussion summary, any delay or abort points used, bridge log entries. | Grounding risk |
| 4 |
Restricted visibility or heavy traffic
Prioritize collision avoidance discipline.
|
Increase radar plotting discipline, reduce speed as required, widen CPA policies, call the master early if uncertainty grows, avoid “automation bias” from a stable looking GNSS plot. | Continuous radar monitoring and plotting, cross-check gyro and log consistency, verify radar overlay alignment behavior, confirm if multiple receivers disagree. | Radar plot snapshots or logs, CPA/TCPA decision notes, visibility conditions, communications, any maneuvers taken and why. | Visibility |
| 5 |
DP or close-quarters station keeping
Treat integrity issues as a control-system input risk.
|
Escalate to DP procedures, verify reference systems, downgrade unreliable references, increase redundancy awareness, prepare for fallback mode or abort criteria. | Confirm reference quality indicators, compare independent sensors, verify time source integrity, monitor position residuals and alarms. | DP alarms, reference status at time of event, actions taken (reference deselection, mode changes), and operational impact notes. | Control |
Proof package checklist, what to capture while it is happening
A lightweight evidence set that supports internal review, insurer questions, and formal reporting
Minimum log set
Time window
Start time, end time, duration, and whether symptoms were continuous or intermittent.
Location context
Position region, nearby hazards, traffic density, and operating mode (open ocean, coastal, approach, pilotage, restricted visibility).
Symptoms
Position jump, loss of fix, integrity alarms, radar overlay mismatch, AIS inconsistencies, multi-system disagreement.
Cross-check outcomes
Radar ranges and bearings, DR comparison, visual bearings, echo sounder consistency, receiver comparison results.
Actions taken
Speed changes, course changes, margin widening, master call, pilot-master discussion, any delays or abort points used.
Screenshots and snapshots
Bridge displays
ECDIS alerts, GNSS receiver status pages, radar overlay view, conning screen where available.
AIS context
Evidence of inconsistent AIS positions or duplicates, paired with radar truth notes.
Data exports
If available, export raw receiver logs and alarm history, note the exact system time source.
External reporting and internal notifications
Internal
Notify company DPA or security contact per SMS, include time window, region, and operational impact.
Industry reporting
Use established reporting channels such as NAVCEN GPS problem reporting and relevant maritime advisories, where applicable.
Language discipline
Describe observations and cross-checks. Avoid asserting intent. Use “suspected interference” unless proven.
Evidence capture should not distract from safe navigation. Assign roles, one person maintains the record while the bridge team prioritizes control and collision avoidance.
Long-term resilience is built before the vessel enters a degraded GNSS zone, by tightening bridge procedures, practicing cross-check routines, hardening time and position inputs where possible, and making reporting and evidence capture a normal workflow instead of a one-off scramble. Recent guidance and advisories make the same point from different angles, expect interference, plan for it, and report it through established channels so patterns can be recognized and warnings improved.
Preparedness and hardening, what operators can standardize fleetwide
Focus: fix discipline, clear roles, evidence capture, and an escalation path that is used in drills before it is needed
Management rule: if the ship has not practiced degraded-position navigation and logging, it will happen ad hoc. Build a simple drill, then make it repeatable.
| # | Readiness area | Ideal | Where operators get surprised | Verify | Tags |
|---|---|---|---|---|---|
| 1 |
Voyage planning for interference zones
Assume degraded GNSS can occur in some corridors.
|
Passage plan includes a degraded-position posture, margin policy, and abort points for confined waters, plus a note on how fixes will be validated without GNSS. | Plans rely on a single “clean track” assumption, or lack a clear trigger for slowing, holding, or delaying pilotage. | Bridge instructions include explicit degraded-position triggers, and they are briefed before arrival. | Plan |
| 2 |
Fix discipline and cross-check routine
Quick, repeatable cross-checks under time pressure.
|
Bridge team can rapidly anchor truth with radar ranges and bearings, DR discipline, and a known set of independent cross-checks that are used routinely. | Cross-checks exist in theory, but are not practiced, or the team does not know which sensor is feeding integrated displays. | Drill outcomes are documented, and the logbook language is consistent across vessels. | Ops |
| 3 |
Integrated bridge time and position governance
Bad time can cascade into multiple systems.
|
Clear understanding of the time source and position inputs, with a known fallback behavior, and a way to isolate suspect inputs when anomalies appear. | Multiple systems disagree, and the bridge cannot quickly determine what is authoritative versus derived. | Documented “source of truth” mapping for key systems, and a basic isolation procedure. | Systems |
| 4 |
DP and close-quarters procedures
Treat interference as a control input risk.
|
DP procedures define actions when reference quality degrades, including reference deselection, mode changes, and abort criteria that are actually exercised. | Operators assume “the DP will handle it,” without practiced decision points when integrity flags appear. | Reference quality indicators are understood by watchkeepers, and drills include fault cases. | DP |
| 5 |
Evidence capture and data retention
Proof packages reduce disputes later.
|
Assigned role for screenshots and logs, consistent time window recording, and a simple internal template that is used during drills and real events. | Evidence is incomplete, timestamps are missing, or displays are overwritten before the record is assembled. | Template exists, crew knows where to store outputs, and retention time is defined. | Proof |
| 6 |
Reporting and escalation pathways
Use established reporting channels where relevant.
|
Internal escalation includes DPA or security contact, and external reporting is routed through established channels such as NAVCEN GPS problem reporting when applicable. | Reporting is delayed, or written as a verdict instead of an observation-based account, creating credibility issues. | Contacts are current, reporting language is disciplined, and drills include the comms step. | Comms |
Fleet Readiness Check, GNSS Interference
Fast scoring to identify the next best operational improvements, not a compliance verdict
Select the closest current state. Outputs highlight readiness tier and the top priorities to fix first.
Readiness tier
Developing
Score
Top priority
Cross-check discipline
First fix
Second priority
Evidence template
Second fix
Directional readiness aid only. Bridge team and master remain responsible for safe navigation and any maneuvering decisions.
Operators that treat interference as a routine risk do two things better than everyone else, they practice degraded-position navigation before it is needed, and they capture the evidence and report it through established channels so the wider community can learn faster. For U.S.-linked reporting, NAVCEN’s GPS disruption report is one of the formal routes, and industry advisories also explicitly call for timely reporting when it is safe to do so.
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