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The French navy is going to equip 4 ships with ONERA's GIRAFE quantum interference gravimeters, starting in 2023, based on a prototype developed in 2012:

https://www.capital.fr/economie-politique/la-marine-francais...

One of the goals is to be resistant to GPS jammers.

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Maybe it's explained in the article but my french isn't great

But how would that work to replace (?) GPS?

Submarines have been using gravity gradiometers for navigation for decades. Tom Clancy revealed what was then classified information about these in The Hunt for Red October. They can serve as passive collision avoidance systems or let the navigators use geological features to correct drift in inertial navigation. The later application requires gravity gradient maps. They are useful for submarines because they are completely passive, unlike active sonar that produces a signal others can detect.

Not french speaking but I will guess that by using extremely precise inertial navigation. Accelerometers measure acceleration + gravity. You need to subtract the gravity.

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