1C18

Could you specify what you mean by 1C18? The designation appears in multiple contexts across different domains, and there isn’t a single universally recognized subject by that name. If you can share the field (for example, military hardware, software/technology, transportation, or something else) or provide a context or link, I can write a concise, neutral wiki-style article. If you’d like, I can also draft a disambiguation-style entry that outlines the main possible uses in a few domains.