DD#10 certainly seemed to imply ships being different and designable.
I don't read it that way. If forced to guess, each ship represents the state-of-the-art for your country at the time you start the build: every light cruiser has the best engine, armor, guns, etc. you know how to build.
Of course, in reality, ships (and most military hardware) reflect different design philosophies: the British probably
could have built a fast, well-armored, lightly-gunned ship like the
Scharnhorst, but they chose to sacrifice speed and armor in favor of hitting power. You see similar tradeoffs elsewhere in military design (and design generally): the Japanese were aware of the concept of self-sealing tanks, for example, but decided their Zeroes would be more effective if they were fragile but maneuverable and long-legged. The Americans, by contrast, valued sturdiness over maneuverability in the prewar era, resulting in the F4F Wildcat. I'm generalizing, of course, but you see the point.
Guessing from the screenshots and the diaries, it will be possible to model this sort of philosophical tradeoff in the game, but not through the construction screen. Instead, your decision to focus research on improving certain aspects of performance over others will be reflected in the models you can build: historically-minded American players can devote research to techs that improve aircraft armor while their Japanese counterparts can devote research to techs that improve aircraft maneuverability (assuming aircraft have those two stats), and the models they can build will reflect those priorities. The historical preferences may be able to be reinforced by the starting tech skills, giving the Americans a pre-existing bonus to research improving aircraft armor and the Japanese an equivalent bonus to aircraft maneuverability research. However, I'm not sure how well the granularity of the research system -- which only divides tech skills into a relative handful of specialties -- will work for this purpose, especially since I haven't seen any indication that techs can use more than two tech specialties to speed research. I count from the tech screenshots 14 techs that might arguably be involved in aircraft research alone: aeronautics theory, practical piloting (possibly gained from combat and used only for air doctrine research), fighter/CAS/medium/naval/strategic theories, practical single-engine/two-engine/four-engine, CAG theory and practical, electronics, and chemical engineering. If each tech can only benefit from a maximum of two of those categories, then there either have to be a lot of techs or you're not going to get a huge amount of granularity.
Again, this is all uninformed guessing, especially about the two-specialty limit to research for any given tech. In HoI2, a tech could benefit from up to five of a tech team's specialties. This allowed a lot of granularity (and also a lot of confusion). I guess this game illustrates another design tradeoff: whether modeling the different design philosophies through the tech specialties is worth the confusing welter of data and multiplicity of choices that would threaten to defeat even avid fans, much less newbies. Or it illustrates I have no idea what I'm talking about, which is probably the safest bet.
