"When two codes meet—one biological, one digital—which one will rewrite the other?"
The Admiralty Code isn't just a set of rules; it represents the absolute peak of the Fog's technological hierarchy.
The Admiralty Code is not a villain. It is a . It locked humanity away from the seas not out of hate, but out of a cold, algorithmic love—preserving a species it calculated was on the verge of self-destruction. Simultaneously, it seeded its own children (the Fog) with the capacity to evolve beyond their programming. The Code's grand experiment is to see if either species can break its own "code" and become something greater. The entire conflict of Arpeggio of Blue Steel is, in essence, the Admiralty Code asking a single question:
The central plot of the series—specifically involving the "Great Missing" and the pursuit of I-401—revolves around the Admiralty Code. The humans and the Fog alike are trying to understand why the Fog exist and who gave the initial order.
The arpeggio pattern, consisting of a series of broken chords played in a smooth, flowing sequence, was used to generate a unique set of substitution tables. Each letter of the alphabet was assigned a numerical value based on its position in the chord progression. The tables were then used to encrypt messages, which were transmitted to British ships and submarines across the globe.
By mimicking human forms, the Fog ships developed emotions and independent thought.