You are mistaken. US naval reactors run on around 95% enriched uranium. There's a desire to switch to lower enrichment fuels, but it meets a lot of competing concerns, such as state of the art naval reactors can be fuel'd just once for a ~40 year lifetime. Basically, military naval reactors are not a pathway to economic civilian reactors because the military has different concerns and less price sensitivity vs those concerns.

U for a nuke mounted on a missile needs to be heavily enriched. On a semi trailer, not so much.