Consular officers at posts abroad face a range of difficult duties including informing relatives of a death abroad, counseling and helping victims of crime (do NOT go into Moscow's underground street crossings late at night), visiting citizens arrested and jailed, refusing visas and dealing with the angry losing parent in a child custody fight. Still, we get a generous share of delightful duties like issuing passports and certificates of birth abroad, issuing adoption visas that give a child a route out of an orphanage to a family in the United States and informing an individual of an unknown claim to American citizenship.
Citizenship laws and regulations changed several times in the twentieth century largely in response to court cases that favored granting or restoring American citizenship by removing restrictions on acquisition and actions resulting in loss of citizenship. Often those cases come with compelling back stories.
For some years a citizen born abroad was obligated to meet a residence requirement to retain citizenship. However, under the doctrine of unawareness and the details of 7 FAM 1100, Appendix K (no more citations after this one) not knowing and the "impossibility of performance" created a kind of second chance. A man in his late 40s, whose U.S. citizen father had served in combat in the US Army in WWI before returning to Poland, brought his mother to Consulate General Krakow hoping she qualified for a widow's pension. An alert Polish employee informed him that he had a claim to U.S. citizenship despite never having lived in the United States. Stunned, he refused to believe her until I assured him it was true. The Bureau of Consular Affairs quickly concurred and two weeks later he had his first U.S. passport and filed an immigration petition for his son before departing for America. It was a particularly rewarding outcome for a family that had been relocated to Siberia during WWII and with difficulty returned to Poland years later.
For a comparatively brief period a woman who married an alien lost her American citizenship, while a woman who married an American obtained American citizenship. In that period of heightened nationalism, the United States and other countries rejected the concept of dual nationality with the husband's nationality controlling. A Costa Rican grandmother, who had obtained previous visas to visit a son and grandchildren in the United States, had a married name that was definitely not Costa Rican. When I queried her about her late husband, she told me he was an American. Bring me that old shoebox full of documents and pictures, I proposed, because I think you are an American citizen and need to travel to the United States on a passport. Her son, irritated by what he thought was about to result in a visa refusal, elbowed past her to the window to complain. "Your mother and I are discussing her American citizenship," I announced. Later when she came with her documents that, indeed, confirmed her claim and received her passport, he also came back to thank me profusely.