Henry,
Last Saturday, Brazilian newspapers reported that on the bottom of the Baltic sea it was found a British submarine that was sunk during the first world war. She left her base on May 31, 1916, and it's believed that sinking happened on June, 1916.
The submarine was in good state of conservation; the possible reason is that the Baltic sea water has little salinity and little dissolved oxygen, so is less corrosive than usual sea water. She belonged to the M13 class and the crew was made up of 3 officers and 15 sailors.
As the German navy during the first world war didn't announce having sunk a British submarine in the Baltic sea during June, 1916, it is believed that sinking occurred because the submarine was navigating on the sea surface and hit a German mine.
The submarine was detected months ago, but it was only last week that the divers could reach it.
Well, that's all Brazilian newpapers said about that.
Giovanni S. Crisi
Sao Paulo - Brazil