I was a little past this point when the sub went down:
I checked in the RSRDC campaign files and that is at the northern edge of a japanese minefield. I could be a coastal gun on the island to the NW which I could plainly see, but I was at radar depth so only my radar was above the surface. The hit took the hull to 32% damage and caused flooding in the control room, conning tower and forward torpedo room. I was on the radar when it happened tracking the ship so I presume I would have had a warning of incoming aircraft? A mine does look like the likely suspect. Just have to be more careful next time.