Last night I was doing the convoy attack exam to re-acquaint myself with SH3. I had penetrated to the centre column & sunk the lead escort. I hit the C2 with a torp, but only managed to damage, not sink it. Then I manoeuvred to get my stern tube to bear on the ships in the outer column.
I guess I concentrated too much on the map, when I took a look ou tthe periscope I saw nothing but the hull of a ship.
This was how close I was to colliding with it. fortunately emergency back & full left rudder prevented an embarrasing incident