Birth aboard aircraft and ships

The subject of birth aboard aircraft and ships is one with a long history in public international law. The law on the subject, despite the provisions of Article 3 the 1961 Convention on the Reduction of Statelessness, is complex, because various states apply differing principles of nationality, namely jus soli and jus sanguinis, to varying degrees and with varying qualifications.

Historical background
Prior to the 1961 Convention, quite a number of states expressly provided, in their laws, that births and deaths aboard an aircraft registered to that state are considered to have occurred on national territory, and thus the nationality laws of that territory apply. One such was § 32(5) of the British Nationality Act 1948. However, this did not solve the problems caused by dual citizenship and conflicts with other states claiming equal competence through the application of the jus sanguinis principle.

Contemporary laws
Under the 1944 Convention on International Civil Aviation, articles 17–21, all aircraft have the nationality of the state in which they are registered, and may not have multiple nationalities. For births, the law of the aircraft's nationality is applicable, and for births that occur in flight while the aircraft is not within the territory of any state, it is the only applicable law. However, if the aircraft is in or flying over the territory of another state, that state may also have concurrent jurisdiction, and the locus in quo principle may apply to the exact position of the aircraft when the birth occurred.

There are still very few Member States that are party to the 1961 Convention. Furthermore, conflicts of laws still exist, in particular between the laws of North and South American states, which typically adhere to the jus soli principle, and the laws of European states, which usually adhere to the jus sanguinis principle.

United States
U.S. law holds that natural persons born on foreign ships docked at U.S. ports or born within the limit of U.S. territorial waters are U.S. citizens. An important exception to this rule is that children born to people who (in line with the Fourteenth Amendment to the United States Constitution) are not "subject to the jurisdiction" of the United States (e.g. diplomats accredited with the United States Department of State) are not automatically U.S. citizens. Despite a common misconception to the contrary, birth on board a U.S.-flagged ship, airliner, or military vessel outside of the 12-nautical mile (22.2 km/ 13-13/16 st. mi.) limit is not considered to be a birth on U.S. territory, and the principle of jus soli thus does not apply.