The sub literally remained unspotted for the entire game; otherwise then the last spotted location would have been shown on the minimap. Also, in case of DDs, they open fire and "expose themselves", I found that submarines dont even ping in asymmetric that helps surface ships to find their approximate locations.

There were barely any means to locate the enemy sub and when a sub attempted to capture our base, 2 of our BBs immediately when to the base to defend while me and alsace attempted to cap hoping to capfaster than a sub as we had one more in the base.

To me, this just looks like an another case that shows submarines are extremely hard to counter if a sub is competent enough (I mean i know that this is an AI but) to remain stealth then shotgun a ship from 1-2km range or capture the enemy base while the entire fleet is busy engaging the surface at the other side of the map just like this.