Slitherine

One of my cruisers were attacked by a sub.
I had a destroyer nearby and did a sonar sweep.
The only sub in the area is clearly outside the US 2-hex torpedo range, right?

Could it be a second sub to the NE?

Doubt it. A 2-range US sub should be picked up by the original sonar sweep.
Especially if it fired the previous turn.

There's 2 or 3 hexes it could be on the right not being touched by sonar...

when in doubt, use god view to double check, i would, then you know what it is, and what it isn't