I wonder why you don't use more of the ships from the Asset Store package you are using. (especially the german ones) Will we see a pacific theater soon? You could use the japanese ships that you should already have from the package.
https://www.assetstore.unity3d.com/en/#!/content/2726
A funny side note: I've asked Mighty Vertex Games if they could create some WW2 ships for the Asset Store or what it would costs to hire them to create 3D Models for me (to speed up things). They've released this package a few weeks later (but I never bought it because the style does not fit to my own models)