Hi Mark,
That’s a really great question. I did a little bit of research into this, and it looks like our current UPS module doesn’t actually have any native support for for military addresses.
This isn’t a specific area I am an expert in, but if I understand correctly – it’s simply a matter of setting the proper ZIP code, having “AE/AA/AP” available as regions and APO/FPO/DPO as “cities”.
After doing a bit more research, it does appear that USPS is the only method possible for shipping to military addresses –> https://answers.yahoo.com/question/index?qid=20061105013404AAPYrjn
That said, if you’re able to switch to USPS and add those AA/AE/AP regions to the database (which I believe is possible via this plugin) – I think you might be in business.
Finally, I’ve added this as an issue to our GitHub tracker. I would love to see better support for this in our core platform. Thanks so much for the question!