The first supplement to When the Navy Walked is now available as a PDF from Wargames Vault. Entitled When the Navy Walked: Conflict on Mars!, the new book adds details on the setting, some new rules for aerial combat and weather, two new unit types (Creatures and Behemoths), additional races, new scenarios, more armies and new Edges and Flaws that can be used in any game of When the Navy Walked... That's an awful lot of stuff to pack into one book!
I am the editor for this product (as well as the second edition of the Core Rules), and honestly, I think we did an even better job with this first supplement than the Core Rules. Not that there was anything really wrong with the Core Rules! But, I keep noticing minor imperfections that just make my editor's soul cringe. I haven't gotten my copy of the final product of Conflict on Mars!, with art and everything in it yet, but I have seen a few peeks and previews of it, and it should be a great product.