The front page states that this is supposed to be late-1800's technology level, in a steampunk setting. There is currently a bit of debate going around regarding the fact that certain nations are more advanced than they should be, and that is the source of the time line confusion.

Ironclad ships would probably be just in the process of arriving in naval warfare, and I could see some of the most air-focused folks imagining ironclad airships, but it isn't something that can be so easily realized. Whoever has Ironclad Airships is going to completely dominate the air war, and air superiority in a setting where air travel has just reached its golden age completely breaks the balance of the game.