GPS jamming is a major liability for US and Allied forces which depend on the system for everything from troop movement to missile and drone guidance. While Trident juncture was taking place the military started noticing that the GPS signals were being jammed, which Finland and Norway officials attributed to Russia and the US officials said that the Russian military had been jamming the GPS system.
The army is currently looking into developing a new generation of Inertial Navigation System that could be used as a back-up. Drones are particularly delicate and can be rendered useless is these signals are blocked and these will cause these devices to malfunction or crash. How the US army intends to go around that is by carrying out testing to figure out what thing works and what thing doesn’t.