Hello Ken,

As a first introduction to your question, please have a look at :

[www.dutchsubmarines.com]

OR : [en.wikipedia.org], and other (Google) sites, same input.

The story of this (Finish) VESIKKO - sub is very interesting re. the way Germany developed this weapon after W.W.1 and despite the Treaty of Versailles.
Regards,
Freddy.