Many years ago I did some research on the S-class because I was curious too. I think I found that the correct S-boats - the boats that saw service in the Pacific during WW II are in SH4. I used 'Silent Victory' and DANFS (online website) as my sources.
You would need 3d modeling skills to build the old R & O class boats, that as you say were only used as training subs by the US.
We very were lucky that Team Keltos built the V-class NARWHAL bonus mod. If you could somehow build the models of the 20's boats you want, I suggest you study the NARWHAL bonus mod to see how he did it. That would be a big project... interesting idea, way beyond me, plus I don't have the software.
Welcome, AdamDizzy, and Happy Hunting!
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Through lonely hours their vigil keep.
May peace their mission ever be,
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Bless those at home who wait and pray,
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