In May 2022, Finland announced its intention to apply for NATO membership. Assuming Finland becomes a NATO member, what does that mean for Åland? Åland is an autonomous and demilitarised region of Finland (and has been since 1856 in the aftermath of the Crimean War). Can Finland meet both its NATO obligations and the obligation to keep Åland demilitarised, or will either have to be adapted? It seems the question has been raised, but I can't find an article outlining possible scenarios.
If Finland were to join NATO without a change in Åland’s status, this would not be the first time that the alliance has incorporated a country with demilitarized zones. The islands of Svalbard retain their status as a demilitarized zone in spite of the fact that Norway is a member of NATO. Svalbard’s demilitarization is based on international agreements similar to those that govern the Åland regime. In the 1920 Spitsbergen Treaty, which confirms Norway’s title to the islands, Norway undertakes not to establish or permit the establishment of any naval base or fortification in the zone. The treaty states that the area may never be used for military purposes. When Norway entered NATO, Svalbard was placed under NATO command, but the demilitarization provisions continued to be observed. [...]
Other examples of demilitarized zones can be found in the Greek islands. Corfu and Paxoi in the Ionian Islands and the Aegean islands of Chios, Lesvos, Limnos, Nikaria and Samos have all been demilitarized through international treaties. [...] In these cases, too, NATO membership in itself has not created any pressure for an end to demilitarization. In Åland’s case, the islands’ fate could be decided in the bilateral membership negotiations between Finland and NATO, but it seems more likely that NATO will choose not to demand a review of the Åland Convention.
For the more complicated scenarios in which the signatories of the 1921 convention (which doesn't include Russia [or the USSR]) collectively decide to abandon that neutral status for the islands... read the paper, but it seems unlikely to me that kind of step would be taken. Finland is also obliged separately to Russia/USSR through the 1940 peace treaty with respect to the status of the islands (although the paper doesn't detail those terms. Actually, the reason for the latter is that the 1921 convention is much more detailed in what is and isn't allowed in and around the islands [e.g. number of ships and tonnage], whereas the treaty with USSR only had very general provisions of demilitarization and non-fortification. See https://www.doria.fi/handle/10024/119970 for details.)