[Capt. Morgan]

I've had a similar experience. Anchored ship, clearly visible, but unable to lock on - even at 1200 yds.

Sent her 2 torps. anyway, and she exploded nicely and went to the bottom, but no "she's going down" message, no tonnage, and no red ship icon on the map even though I watched her sink.

I'd guess is that it's a game glitch. I did notice that she was so close to the shore that when I zoomed the map out, her position was indicated as being on land, so maybe it happens if a ship spawns in the wrong place