Interference with satellite-based navigation systems such as GPS has become more and more common. Since the outbreak of war in Ukraine, warnings about GPS interference have become more frequent, including from European aviation authorities. Navigational warnings point out risks in large parts of the Baltic Sea, the Gulf of Finland and the Sea of Åland. On several occasions, GPS signals have been seen to disappear completely, or vessel positions have been seen to move in unnatural patterns and at unnatural speeds. Shipping is therefore urged to watch for deviations in its systems and to always have alternative aids available in case the signal disappears.

Different methods of interference

GPS can be disrupted by what is known as jamming and spoofing. This means that signals are knocked out or replaced with false information. This can have serious consequences, especially if the interference is carried out with hostile intent and is not detected on board. Incorrect position data can lead to collisions or groundings, putting lives, property and the environment at risk. It can also mean that you cannot give your position if you are in distress.

The Coast Guard's measures and preparedness

We have procedures and training that allow our crews to carry out their tasks safely, even in a disrupted environment without GPS, by using alternative methods of navigation and position fixing.

The Coast Guard continuously reports interference and works with authorities such as the Swedish Maritime Administration, the Swedish Civil Defence and Resilience Agency and the Swedish Transport Agency to follow developments and take action when needed.

The ability to navigate under disrupted conditions is teamwork. It requires clear division of roles, an active culture of questioning and a shared situational picture in which uncertainties are stated clearly. A robust navigation capability that does not depend on GNSS is an important part of the Coast Guard's operational credibility – in peacetime, in the grey zone and during heightened alert.

Tips for navigating without GPS

Coast Guard crews regularly notice GNSS interference. Our advice to others who work at sea is to be aware of the problem and never to rely only on navigation equipment that is integrated with GNSS.

  • Write down your position and speed regularly, so that you can state them if you need help
  • Bring paper charts, a compass and a VHF radio
  • Choose a route that you know well
  • If you have radar, use it

Glossary

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