By law, a valid unexpired U.S. passport (or passport card) is conclusive (and not just prima facie) proof of U.S. citizenship, and has the same force and effect as proof of United States citizenship as certificates of naturalization or of citizenship, if issued to a U.S. citizen for the full period allowed by law. sub-type of regular passports is no-fee passports, issuable to citizens in specified categories for specified purposes. For example; an American sailor, for travel connected with his duties aboard a U.S.-flag vessel. Period of validity: generally 10 years from the date of issue.