Probably the best bet considering how most Finnish submarines served as prototypes for various German submarine-classes (Vetehinen-class being prototype for Type VII and Vesikko serving same purpose for Type II), with, in the extremely unlikely scenario that Finnish Navy ever appears in KC, either Vetehinen-class' nameship (sunk a Soviet submarine by ramming it) or Vesikko (preserved as a museum) being the most likely candidates.
Probably the best bet considering how most Finnish submarines served as prototypes for various German submarine-classes (Vetehinen-class being prototype for Type VII and Vesikko serving same purpose for Type II), with, in the extremely unlikely scenario that Finnish Navy ever appears in KC, either Vetehinen-class' nameship (sunk a Soviet submarine by ramming it) or Vesikko (preserved as a museum) being the most likely candidates.
I think Vesikko is too small a sub to appear in Kancolle, and the Väinämöinen Class is too underpowered. Vetehinen would be a fair choice, for that ramming kill.
Well, Maru-yu has displacement close to Vesikko, but Vesikko can submerge...