Britain's Maritime and Coastguard Agency has told shipowners that satellite navigation can no longer be taken for granted in some of the world's busiest shipping regions, and crews must practise navigating without GPS as jamming and spoofing spread.

The warning, published as Marine Guidance Note MGN 719, states that interference across the Baltic, the Black Sea, the Middle East Gulf and parts of East Asia means satellite-derived positioning, navigation and timing data can no longer be relied upon everywhere.

The numbers behind the guidance are stark. Windward's latest figures show an average of 5,131 GPS jamming incidents a day during the third quarter, with more than 124,000 individual vessels affected. That is no longer a fringe hazard in conflict zones. It's a routine operational condition.

What does this change for operators?

The MCA's scope extends well beyond electronic charts. The agency names a long list of vulnerable bridge equipment:

• ECDIS
• AIS
• autopilots
• dynamic positioning systems
• radar
• gyrocompasses
• GMDSS communications equipment

Ashore, vessel traffic services, pilotage systems, port management platforms and automated logistics systems are also exposed. In other words, the risk runs from the wheelhouse to the terminal gate.

The financial exposure is considerable. Citing earlier UK government research, the MCA estimates that a seven-day GNSS outage could cost the British maritime economy £1.5bn ($2bn), including £1.3bn in port operations alone. Ports, not ships, carry most of that bill.

What is the guidance asking crews to do?

MGN 719 urges operators to identify precisely which onboard systems depend on satellite-derived data, establish procedures for detecting interference, and regularly drill crews in alternative navigation methods. The recommended fallbacks are traditional: radar fixing, visual bearings, celestial navigation and dead reckoning.

The notice lands after growing evidence that interference is becoming a persistent operational hazard rather than an occasional inconvenience. Research published earlier this year by the Royal Institute of Navigation found that 14% of survey respondents had experienced an unsafe or unlawful situation resulting from GNSS interference.

In July, SplashTech reported on a government questionnaire, believed to have originated in Britain, asking ship operators three pointed questions: whether their crews had conducted GNSS-denial drills, whether they understood the vulnerabilities of interconnected bridge equipment, and whether they could operate ECDIS in dead-reckoning mode.

The spoofing cases have grown more dramatic. Four tankers in the Black Sea apparently broadcast positions placing them in Lima, Peru — more than 12,000 km away. Separate monitoring identified 1,702 impossible position jumps involving 379 vessels in the Gulf of Oman over a single week in September.

When will a backup arrive?

Not soon. The UK is investing in a terrestrial navigation backup through its enhanced Loran, or eLoran, programme, but the MCA's guidance makes clear that technological alternatives will take time. Britain's planned eLoran network is not expected to provide an initial timing capability until 2028, with full positioning and navigation services targeted for 2030.

That leaves a gap of several years in which crews sailing the Baltic, the Black Sea and the Gulf must fall back on skills and procedures. For shipowners and their insurers, the message is that GNSS resilience is now a compliance and training issue, not an IT footnote — and the drills the MCA wants will need to happen long before eLoran switches on.