My "Complete Works" of Kipling is the version with the sickeningly sycophantic commentary. I don't intend to subject myself to the torture of reading that again, but I recall it describes "Files-on-parade" as a Greek chorus, always asking the right questions to enable the protagonist (the Colour-sergeant) to say what needs to be said.

"File" as in "rank and file", "single file", etc.

Killing anonymous enemies in the heat of battle is a world away from being made to watch the cold-blooded execution of a comrade, far removed from the violent passion of his crime. The front-rank/rear-rank are moved by the powerful emotion of the situation; the colour-sergeant excuses their reactions by inventing reasons, in that "I'm your mother now!" way that they sometimes have.

Steve