My 2 cents:
If SH4 uses the updated engine from SH3. Include all german U-Boats from SH3, but only Pacific theater. If it's the same engine, this should'nt be a lot of work. But it would mean that the community could mod the Battle of the Atlantic with all new features - so everyone would be happy. Right now the only thing in the way to model new TOO's is sub interiors.
If SH4 uses a new engine, I don't expect it having German subs. Which would be a pity because many people wouldn't buy it or end up disappointed with Sh3.
As to Japanese boats. Realistic or not, bring them on UBI! I am madly in love with everything Japanese. Their technology during WWII might not always have been up to standard, but the exterior design looked absolutely sexy! Just look at some Japanese WWII planes and you'll know what I mean.
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