Russian forces are expert at jamming and spoofing GNSS. As a result, military analysts say, Russian military doctrine assumes that signals from space, including it’s own GLONASS and other GNSS (EU System) , will not be available once a battle begins.

According to the Russia and CIS Radionavigation Plan, the terrestrial Chayka system, a version of Loran-C, is maintained to protect their homeland


https://www.gpsworld.com/russia-expected-to-ditch-glonass-for-loran-in-ukraine-invasion/
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