Grey "sunken ship" icon on the map? Fellow UBoat i
 

I got a sound contact from a warship travelling away at high speed, about 25 km out. Then a minute or so later, a grey "ship sunk" icon showed up on the map on the general area of where the warship was. Was this a fellow uboat that got sunk? It was in the "hunting grounds" just NW of Ireland, so I doubt that a German warship or even a German merchant would've been in that vicinity. Any ideas? I also had another similar occurence later in the same mission in the other "hunting grounds" just South of Ireland. Any ideas??

Grey contact sunk icons are ships that were sunk by the weather usually.

Bad Weather seen it happen.

Grey sunken ship icons are unidentified ships that sank within detection range. Mostly they are due to bad weather, but I think it could happen if a ship sinks for whatever reason before you've identified it visually.

I've seen destroyers run into docks and sink while hunting me in allied ports and they show up as grey icons.

Tosh saw an enemy merchant red on my map watched it sink in bad weather and on my map turn from red to grey.

OK that explains it! Thanks for solving that enigma (no pun)