Volokh has an interesting examination of case law regarding whether knives are "arms" for Second Amendment purposes.
A lot seems to turn on whether a class of weapon is regularly used in "civilized warfare." That standard would seem to make it proper to carry a Kabar, since it was military issue and is still regularly carried by soldiers, sailors and Marines...
...but not a Buck knife, which is primarily for hunting. Yet the design is substantially the same, except the Buck 119 Special is a little shorter.
It's nice to know that swords still turn up as 'weapons of civilized war.' They're not as random or clumsy as a handgun, either.