The imagery of Gremikha was changed with one of the recent updates and is of a lower quality than the previous imagery. Sadly, the 'sub wreck. 620' is now less clearly visible. I think this wreck is the WWII S-class submarine S-51. The S-51 was stripped of its outer hull and left on the shore near Gremikha. The outer hull was used to construct a submarine memorial in the town nearby. This website has photos of both the wreck and the memorial.