I don't know much about militaries or nuclear reactors, but I know that reactors are used in some submarines and in some aircraft carriers -- situations where you want a vessel to to remain at sea for long periods of time without refueling, and weight is not a primary concern.

That's pretty niche, though. Think about trucks, tanks, aircraft, generators for outposts, etc. It might be cool if you could safely package a zillion nuclear reactors for those use cases, Terminator style, but I'd guess that reactors are a better fit for centralized, permanent power generation.