[Barrin92]

>Perhaps EU or China could build their own network of sensors to track this stuff?

already do, the EU is in particular collects a ton of oceanographic data through for example the Copernicus Marine Service, but these particular sensors are in waters close to Oregon, Washington and Alaska, not really anything the EU or China could replace.

In its region the US is naturally not really replaceable, it's simply a big blow to research.

[pvaldes]

China will happily jump to help.

To help themselves to be able to track the movements of US nuclear submarines anywhere in waters close to Oregon, Washington or Alaska (Or to move their own submarines freely by the area without telling to anybody except them).

Dismantling sensors around Alaska helps Russia on an hypothetical future attempt to retake the area; and doing it around "51 state" or Greenland is the same thing for US.