I'm re-reading Rules of Engagement, one of the Horus Heresy short stories and I'm confused.
This is the story of the 4th Company adopting the Codex Astartes and following their Primarch's tactics.
What I don't understand is why they're fighting (and killing) the Salamanders in one of the engagements? Both legions remained loyal!
I did consider that this may be a training exercise
like the last one where "Horus" turned out to be Roboute Guilliman in disguise
But I don't believe that's the case as they've previously fought Death Guard and World Eaters who are most definitely traitors!
Why were the Salamanders the target during the engagement? Were they a traitorous company or was something else going on?