http://www.richw.org/dualcit/cases.html#Mandoli 

Mandoli v. Acheson, 344 U.S. 133 (1952)

Joseph Mandoli was a dual US/Italian citizen by birth (born in the US to Italian parents). He left the US as an infant and moved to Italy with his parents. When he sought to return to the US in 1937, his claim to US citizenship was rejected because he had failed to return promptly to the US upon reaching the age of majority, and also because he had served briefly in the Italian army in 1931.

The Supreme Court ruled that the law, as it then stood, did not permit natural-born US citizens to be stripped of US citizenship for failing to return to the US upon reaching adulthood.

The court did not base its ruling in this case on any overriding constitutional arguments. Rather, it examined the legislative history of the portions of US citizenship law, and concluded that Congress had consciously chosen to make these provisions applicable only to naturalized US citizens (see Rogers v. Bellei below).

In particular, the court noted that although US law at that time required certain US citizens with childhood dual citizenship (such as those born abroad to American parents) to make a specific "election" of US citizenship (i.e., a declaration of allegiance followed by a return to the US) upon reaching adulthood, no such requirement applied to a person who had US citizenship on account of having been born in the US. Lower courts had apparently interpreted the Supreme Court's earlier decision in Perkins v. Elg as imposing such an "election" requirement quite broadly.

The court also decided that Mandoli's foreign military service did not warrant loss of his US citizenship because, under Mussolini's Fascist government, he really had had no choice but to join the Italian army.

Dean Acheson (Dean was his first name, not a title) was Secretary of State during Truman's second term as President.

[go to the full case on FindLaw]