Very minor…but some reason that line doesn’t convey the same tone as what precedes it. Goes from “hellish”…which sound grim and brutal…to “nastiest”…which I dunno just sounds kinda lame. Mosquito bites are nasty, rotten eggs are nasty…deadly enemies of the empire should carry a little more dread than that 
I’d personally write something like:
Combat Mastery (name not finalized)
In the imperial army, Soldiers are trained to survive in the most hellish conditions and hold the line against the brutal/vicious/demonic/imposing/deadly/unrelenting/savage/mortal/wicked/bloodthirsty/ferocious* enemies of the empire
*choose one 