A friend made me aware that I'm writing TAK everywhere but in the army the sectorial is named TAC (Tartary Army Corps). And when I look around I see it everywhere. Anyone uses TAC at all? Is this a case of the presentation of the sectorial being spoken so no-one noticed when the it was written with a C? Or is it named TAK in Spanish?
I think it's that it would be "TAK" in Russian. The initials for a sectorial seem to follow the native language ordering. Maybe someone who knows Russian could confirm?
I have been learning to speak Russian for several years now, and I think that @Káosz Brigodéros has the right idea. Russian only has one letter that makes /k/ sound (К), unlike English and (to my limited knowledge) French, which will preferentially use a C to make that sound. So the TAK acronym is probably a result of transcribing the Russian Тартарскйи Армейский Корпус into Latin characters.