I’m pretty sure Martin Helsdon covers this in more detail in Armies and Enemies of Dragon Pass, but here are some notes for writers or GMs who want to have Lunar units in their games:
Most Heartland Corps regiments in the Lunar Army are organized around a file of 25 soldiers, each of which composed of three detachments (or somewhat confusingly called a “half-file”) with six regular soldiers within it and one standard-bearer or detachment leader. Attached to the file is an officer, the guardian, and two aides for the officer. The guardian is under the command of the officer and they cast spells for the file. The guardian is always provided with extra magic points.
Common spells cast by the guardians might include Speeddart, Coordination, Mobility, Shimmer 4, Fireblade, Protection 4, Vigor, etc., – the specific spells vary by the tradition of that regiment.
Four files are normally lumped together into a company or “hundred” – led by an officer. For convenience let’s call that officer a “captain” or a “centurion”. Captains are most commonly appointed by the regimental commander but they are sometimes appointed by the Red Emperor or his representatives, or even elected by the soldiers. The captain is almost always a member of the Yanafal Tarnils cult (and is often a Rune Lord of that cult). The captain is aided by two aides, a senior guardian (often a Rune Priest), a standard-bearer, and by whatever other companions are traditional for that company.
Ten companies are grouped together into a regiment, such as the Marble Phalanx, the Silver Shields, etc. The regimental commander is appointed by the Red Emperor or his representative, and is almost always a Rune Lord of Yanafal Tarnils. The commander has a personal retinue, including a Rune Priest (who is priest of the regimental cult), several aides, standard bearers, etc.
What that means in your games is that the traditional party of four to six player characters can be opposed by approximately the same number of Lunar soldiers (seven). And as a GM, just make all the soldiers the same except for the detachment leader. If you want to make it tougher, just add from the officer, guardian, the two aides, etc.
This makes it really easy to scale things. For a really touch challenge, the regimental commander sends out part of his retinue (a Rune Lord leading a file of picked troops), and that sort of thing.
The term “guardian” is from published materials.
The truth is that there was no standard number in a phalanx file. A “stichos” or file could be anywhere from 8 to 16 or more. The Lunar group of 25 soldiers is called a file because that’s what it derived from. But now it is clearly three groups, coordinated by an officer. Most likely that is a development from the Third and Fourth Wanes, when the Lunar Army was forced to be extremely flexible and reinvent itself.
Lunar small unit organization is actually written up in the Cradle scenario in the RQ2 / Classic Pavis book. It is called a platoon there, but Greg’s copy scratches out the word and replaces it with “file”. Probably because we talked about how platoon is really anachronistic.
Whether we call the 25 person unit a file or platoon is immaterial. I personally don’t like calling it a platoon since the word comes from firing volleys, but honestly that’s irrelevant.
I like looking at the Greek names for military organization largely because they are so damn imprecise and inconsistent.