Come arcross this yesterday, but some of you may know this already but will redo again.
Dougie Martindale has release to Uboat Achieve his collection of Ubout modeling articles. It has extensive research and construction details of Uboats.
https://www.uboatarchive.net/Modeling/Articles.htm
If this is something well known, then sorry for reposting.
Good hunting,
FUBAR295