hi,
@popol0011 - you have a famous u-boat, U-47 - commanded by Gunter Prien, it sneaked into Scapa Flow and sunk a Battleship, see
http://www.uboat.net/boats/u47.htm
and
http://www.uboat.net/articles/index.html?article=34
Mine, out of interest, is a type II : U-63, and in reality didn't achieve a great deal - being sunk near the Shetlands by a combined RN destroyer and submarine attack
Kaleun