So, here are my suggestions
First of all, you seem to have two models, one for Argonaut and one for Narwhal/Nautilus, which is a great thing.
This model here reflects much better the Argonaut, but the deck gun platform should beat the same level as the deck, and then extending downwards over the hull (As it extends right now):
What I would see as improvement is 1) Lower the deck gun platform to match the deck level, 2) smoothen the areas marked in red, and 3) eliminate the bounce of the saddle tanks marked in yellow. The V-Boats had a hull shaped much closer to a ship than to a conventional submarine, because the saddle tanks did not protude.
Now, this second model is perfect for the Narwhal:
Again I would smoothen the area marked in red and also eliminate the saddle tank or at least smooth it a lot.
The raised deck gun platform marked in green is good, but it would llok even better if it had the holes in 3D (I suppose you were planning to do them as 2D in the texture).
One more thing: Since you seem to be going to retexture the whole new model, you could contact Foofighters for permission to use his Narwhal skin, which was created for the pseudo-Narwhal done by Ducimus, but would fit well in the new model if retextured. That skin was really gorgeous!
I will also make a set of historic single missions for the Narwhal/Argonaut to be added to the download pack!
