it isn't a ship comparable to the current sub's. according to what I read about it, this was an ship that was lying on the bottom most of the time. when a ship was sailing over it, it would launch it's shkval torpedo's.
the ship is not able to float, because it is too heavy. it would move with the large waterjets on the side, which look like it is some sort of harrier propulsion scaled up
the torpedo's are indeed a lot smaller then most, these were shkval's. these released a gas on the nose, so it would travel through gas and not water. becuase of this it was a lot faster then normal torpedo's.