26 C.F.R. § 20.2209-1
As used in this part, the term "nonresident not a citizen of the United States" is considered to include a decedent dying after September 14, 1960, who, at the time of his death, was domiciled in a possession of the United States and was a United States citizen, and who acquired his United States citizenship solely by reason of his being a citizen of such possession or by reason of his birth or residence within such possession. The estate of such a decedent is, therefore, subject to the tax imposed by section 2101 which is the tax applicable in the case of a "nonresident not a citizen of the United States." See paragraph (a)(2) of § 20.0-1 and § 20.2208-1 for further information relating to the application of the Federal estate tax to the estates of decedents who were residents of possessions of the United States. The application of this section may be illustrated by the following examples and the example set forth in § 20.2208-1 . In each of the following examples the decedent is deemed a "nonresident not a citizen of the United States" and his estate is subject to the tax imposed by section 2101 since the decedent died after September 14, 1960, but would not have been so deemed and subject to such tax if the decedent had died on or before September 14, 1960.
Example (1). C, who acquired his United States citizenship under section 5 of the Act of March 2, 1917 (39 Stat. 953), by reason of being a citizen of Puerto Rico, died in Puerto Rico on October 1, 1960, while domiciled therein. C is considered to have acquired his United States citizenship solely by reason of his being a citizen of Puerto Rico.
Example (2). E, whose parents were United States citizens by reason of their birth in Boston, was born in the Virgin Islands on March 1, 1927. On September 30, 1960, he died in the Virgin Islands while domiciled therein. E is considered to have acquired his United States citizenship solely by reason of his birth in the Virgin Islands (section 306 of the Immigration and Nationality Act (66 Stat. 237, 8 U.S.C. 1406 )).
Example (3). N, who acquired United States citizenship by reason of being a native of the Virgin Islands and a resident thereof on June 28, 1932 (section 306 of the Immigration and Nationality Act (66 Stat. 237, 8 U.S.C. 1406 )), died on October 1, 1960, while domiciled in the Virgin Islands. N is considered to have acquired his United States citizenship solely by reason of his birth or residence in the Virgin Islands.
Example (4). P, a former Danish citizen, who on January 17, 1917, resided in the Virgin Islands, made the declaration to preserve his Danish citizenship required by Article 6 of the treaty entered into on August 4, 1916, between the United States and Denmark. Subsequently P acquired United States citizenship when he renounced such declaration before a court of record (section 306 of the Immigration and Nationality Act (66 Stat. 237, 8 U.S.C. 1406 )). P died on October 1, 1960, while domiciled in the Virgin Islands. P is considered to have acquired his United States citizenship solely by reason of his birth or residence in the Virgin Islands.
Example (5). R, a former French citizen, acquired his United States citizenship through naturalization proceedings in a court located in the Virgin Islands after having qualified for citizenship by residing in the Virgin Islands for 5 years. R died on October 1, 1960, while domiciled in the Virgin Islands. R is considered to have acquired his United States citizenship solely by reason of his birth or residence within the Virgin Islands.
26 C.F.R. §20.2209-1