The drone’s goal is to locate it, you’d then send something else to destroy it if you’re in an actual war.

America uses surface buoy’s to similar effect, going underwater would allow drones to be harder to detect. https://idstch.com/military/navy/navy-researching-new-buoy-t...

Of note you don’t necessarily need to be able to track a sub everywhere, an invisible underwater “fence” may be good enough.