[Timpanagos1]

You may read about the FS-240 at this link.

http://travel.state.gov/content/passports/en/abroad/events-and-records/birth.html

[TigerClaws]

https://travel.state.gov/content/travel/en/legal-considerations/us-citizenship-laws-policies/citizenship-and-dual-nationality.html

It states: “Section 349 of the INA (8 U.S.C. 1481), as amended, states that U.S. nationals are subject to loss of nationality if they perform certain specified acts voluntarily and with the intention to relinquish U.S. nationality. Briefly stated, these acts include:

(and # 1 in their list is)
“obtaining naturalization in a foreign state upon one’s own application after the age of 18 (Sec. 349 (a) (1) INA);”

[Yosemitest]

That link DOES NOT ANSWER the RELEVANT QUESTION:

What was the first year that the FS-240 were require/issued at the time of birth?