GPS jamming and GNSS interference in navigational warnings
Written by seahazards · updated 2026-09-24 · numbers recounted nightly
Ships rely on satellite positioning for almost everything, from the chart display to the automatic identification system. When those signals are tested, jammed or spoofed, navigational warnings are one of the few public records of it.
Two kinds of message
Some GPS warnings announce planned events: periods when signals may be unreliable in an area because of testing. Others report interference as it happens — ships losing their satellite fix, or seeing positions that jump, sometimes placing them kilometres inland.
Since the early 2020s, reports of jamming and spoofing have become common in the eastern Mediterranean, the Black Sea, the Baltic, the Persian Gulf and the Red Sea. Warnings capture only part of this: many incidents are reported through other channels, or not at all.
The wording varies between services. Some messages say that satellite navigation signals may be unreliable within a radius of a point for a stated period; others relay what ships have observed. Either way the advice is the same: navigate with caution and cross-check positions with radar, visual bearings and other means.
4,617 messages use it, 1 of them in force now; most often in Gulf of Mexico, Coral Sea, North Atlantic Ocean.
What the archive can show
The glossary counts every message that mentions GPS or GNSS, by year and by sea. The count shows how often the subject reached the warning system — not how often interference occurred. Messages about differential GPS stations going off air are about a correction service rather than the satellites, and are counted with them.
Read a rise in one sea's count as a rise in reporting: a coordinator that starts broadcasting interference notices, or a conflict that makes ships more likely to report, changes the count as much as the interference itself. The collection gap between the NGA archive and live collection also falls across the years when these reports grew, so year-to-year comparisons across it are not meaningful.
Interference also affects the automatic identification system, which reports positions derived from the same signals.
Satellite positioning feeds more than the chart. Electronic chart displays, AIS transponders, the timing of radio equipment and a ship's logs all take their position or time from it, so a spoofed fix can appear consistent across every system on the bridge. That is why warnings about interference ask for independent cross-checks rather than a switch to another receiver.
48 messages use it, 5 of them in force now; most often in North Sea, Black Sea, Persian Gulf.