It's always nice to see an old tech stage a comeback and this time it's happening around the coasts of Europe, with nine low-frequency radio transmitters substituting for GPS' satellite-based system. eLoran's radiowave-based system is stronger than satellite signals and less jammable, based on the Loran system that was previously used for shipping navigation by both the British and US navy over 50 years ago.
Each probe can pick up GPS signals and signals from eLoran, an enhanced version of Loran, the ground-based terrestrial radio-navigation system first used by the American and British navies during the second world war.