Are katanas illegal in the US?

Good day, I'm curious about the legality of katanas in the United States. As a collector of traditional Japanese swords, I've heard differing opinions on whether or not it's permissible to own and possess these swords within the country. Could you please clarify the legal status of katanas in the US? Are there any specific regulations or restrictions that I should be aware of before purchasing one? Thank you for your time and assistance.