French submariners accidentally disclosed information about the maritime patrols of their nuclear-powered ballistic missile submarines through the Strava application.

Le Monde reported about the incident.

Due to the data that the sailors openly published in the program, users were able to learn about the operation of the base on the island of Ile Longue, located in the west of the country, and the schedule of submarines’ duty.

The crews of French nuclear submarines publicly share their sporting activities through the Strava app, inadvertently disclosing confidential information about the SLBM patrol schedule.

Thus, information from one of the French fleet’s most secretive bases, located in the harbor of Brest (Finistère) on the island of Ile Longue, was publicly available.

It is on Ile Longue that four SLBMs are based, each carrying sixteen nuclear missiles, which are about a thousand times more powerful than the bomb dropped on Hiroshima. This is the home of the naval component of the French nuclear deterrent.

The four “black boats,” as they are called, have been operating on a “constant patrol at sea” since 1972, and although their exact location is classified, at least one of them is always on standby.

Their task is to disappear into the ocean and be ready to receive an order from the French President and launch a nuclear strike.

Land and sea patrols and unmanned aerial vehicles ensure the security of this base. More than 2,000 employees have to be vetted to access the site: scanners, facial recognition systems, and sniffer dogs monitor everything that happens, as Le Monde noted during a visit in December 2024.

Cell phones and other electronic devices are prohibited on most of the base and must be stored in special lockers at several checkpoints.

However, even such strict security measures could not prevent the leakage of extremely sensitive information from this fortress. According to the data published in the article, the submarines’ locations were revealed through their jogging routes. At the same time, their schedules allowed for calculating the frequency of submarine deployment for combat duty.

It was through the use of the Strava app that the location of U.S. bases in Syria was revealed, where military personnel jogging regularly and noting their activity made it possible to geolocate their clusters. Subsequently, the US Department of Defense banned its military from using the geolocation function in apps and on any devices in the field.