Yes, it is ethical to put military research to the best use we can. Whether logistical systems, trauma medicine, personal weapons, or encryption, all those improve our efficiency, our safety, our leisure, and our privacy.

Wars aside, the military is a place where practical problems are encountered daily, and the solutions battle-tested at scale. It's reasonably safety-minded and cost-aware (spicy anecdotes aside).

Moreover, it's helps a lot when the research isn't walled off by stringent IP regulations.