This is from an interview with Emmerich that I think I posted earlier elsewhere:
"Well, first of all, there's nothing left. None of these ships are in their wartime condition. Even when you have some aircraft carrier sitting around, like one in Alameda and one in, I think, South Carolina or in New York, they were altered in the '60s. The flight deck is totally different, et cetera, et cetera. And then they have actually put modern technology in some of the flak turrets.
So we knew from the very beginning we had to build everything. The biggest problem we had was that we had make this indoors because we have to shoot everything with bluescreen in order to constantly have the light to change. So that's what we did. We went to Montreal, where they have a very, very big stage, and built a flight deck or part of a flight deck.
We had to build the planes because even like some Douglas SBDs around, but they're also altered. They have to be altered because otherwise nobody would be allowed to fly them. There are no TBDs anywhere because they probably threw all these planes away because they were not such good planes.
So, we had to pretty much create everything. When you can create everything, then naturally you can be absolutely exact. Our aircraft carriers, both Japanese and Enterprise and the Hornet, what you see is super correct because there's endless research material, photographs and stuff.
I did the production design with the same gentleman who also did "The Patriot," Kirk Petruccelli. He's very, very good in recreating historic stuff. He's very into research.
Then, really, I had to work with a lot of organizations. There's a roundtable group about Midway will all kind of people who have a lot of information who helped us to get this all right.
It's a relatively perfect re-creation of everything."
source: military.com