[Hitman]

I can't help you much with that, but at the spanish web u-historia there are excellent articles about the Type XXI under "tecnica/Artículos tecnicos" (Technic/Tech Articles)

I must however warn you that any modern pictures of the only survinging Type XXI "Wilhelm Bauer" will not necessarily be correct, because the sub was extensively modified after the war and the restoration conducted later is not perfect.