In February 2024, Greece and Turkey announced that they would join the German-led ESSI, an initiative to increase air defense capabilities in Europe in the wake of Russia's invasion of Ukraine (Defense News, Deutsche Welle, NATO). A public announcement, letter of intent, or similar instrument would count, though a conditional announcement (e.g., Poland would join if country X does A, B, and C) alone would not count.

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NOTE 11 July 2024: The approval of a declaration of accession like what Switzerland did in April 2024 will count (e.g., Switzerland Federal Council).

The question closed "Yes" with a closing date of 20 May 2024. The question did not close as of Tusk's aspirational comments in April 2024, but rather additional, substantive actions taken in May 2024 (Polska Agencja Prasowa).

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