I could track the movements of enemy submarines despite having no vision nor sonar, through fog of war.
#Once seen, Orca submarine failed to hide their effects in FoW
sour nexus
See the water disturbance near the middle of the screen, that's 2 subs
https://bar-rts.com/replays/8c0cf56875b38cf5f28ed0b054640259
Replay link, but I'll try to reproduce in skirmish a bit later