As per everyone's comments above, all of the models (of ships, AFVs or aircraft) will be the same*, aside from the impact of any companies (which had bonuses based on the company), but players can make variants that are different, and the starting OOBs will include a range of variants to add flavour. All the pictures and models (for the ships, not the planes and tanks, just another example of navies being a second-class arm of the armed forces) look to be the same, but we expect that we can mod in country-specific pics and models. I'm putting together a bunch of data on the starting naval forces, and will be modding in stuff as appropriate to make it more plausible, although want to get a good feel for the game first, so I wouldn't expect anything substantial out of me until after September at the earliest.
*This isn't a bad thing - gives player choice about how they develop their forces, rather than be straight-jacked to design decisions based on a historical situation that may not be reflected in-game.
I hope I don't incur the wrath of the boat junkies for saying this, but all ships look more or less the same to me...

. Go back to your Dorniers

. JJ of course - maybe HoI4 will be the game that gets you to appreciate the difference between flush-deckers and ships with a raised forecastle?

.