I would have a good look at uboat.net for the technical detail.
I would suggest a smaller coastal boat as it would have been easier getting in and out of small coves etc.I would also suggest your friend reads the book Casabianca by Captain J L'Herminier.This was a Free French submarine that did a lot of this type of work in Corsica and he even has a diagram on how to penetrate an enemy blockade.
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