33 CFR § 125.23 - United States citizens.
Acceptable evidence of United States citizenship is described in this section in the order of its desirability; however, the Coast Guard will reject any evidence not believed to be authentic;
(a) Birth certificate or certified copy thereof.
(b) Certificate of naturalization. This shall be presented by all persons claiming citizenship through naturalization.
(c) Baptismal certificate or parish record recorded within one year after birth.
(d) Statement of a practicing physician certifying that he attended the birth and that he has a record in his possession showing the date and place of birth.
(e) United States passport.
(f) A commission in one of the armed forces of the United States, either regular or reserve; or satisfactory documentary evidence of having been commissioned in one of the armed forces subsequent to January 1, 1936, provided such commission or evidence shows the holder to be a citizen.
(g) A continuous discharge book, or Merchant Mariner's Document issued by the Coast Guard which shows the holder to be a citizen of the United States.
(h) If an applicant claiming to be a citizen of the United States submits a delayed certificate of birth issued under a State's seal, it may be accepted as prima facie evidence of citizenship if no one of the requirements in paragraphs (a) through (g) of this section can be met by the applicant and in the absence of any collateral facts indicating fraud in its procurement.
(i) If no one of the requirements in paragraphs (a) through (h) of this section can be met by the applicant, he should make a statement to that effect, and in an attempt to establish citizenship, he may submit for consideration data of the following character:
(1) Report of the Census Bureau showing the earliest record of age or birth available. Request for such information should be addressed to the Director of the Census, Suitland, Md. 20233. In making such request, definite information must be furnished the Census Bureau as to the place of residence when the first census was taken after the birth of the applicant, giving the name of the street and the number of the house, or other identification of place where living, etc.; also names of parents or the names of other persons with whom residing on the date specified.
(2) School records, immigration records, or insurance policies (the latter must be at least 10 years old).