The Submarine I-401 (Submarine) as depicted in Aoki Hagane No Arpeggio. It is the organization Blue Steel's flagship.
While the other members of the Fleet of Fog generally lend their names to their Mental Models (i.e. Personifications), the I-401's own Mental Model has a separate moniker for herself, Iona (Aoki Hagane No Arpeggio), which the people within Blue Steel and its circle also use. This is why the I-401 and Iona have separate tags in Danbooru.