system
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human
(40K) So some questions on Guardsmen casualty figures.

As my battle-brothers and I prepare to bring the Emperor's cleansing light to the heretics and demons on the planet below, I see many of our guardsmen allies being given what seem to be last rites. I began to wonder how many of them would fall in our coming battle. I know millions die in any given engagement, but how many is that in comparison to their total number? A mere 5% or a devastating 95%, and if the latter how is this system sustainable? I know that average life expectancy of a guardsmen is 15 hours in a combat zone, but surely not all their great number are in a combat zone, some must be fortifying positions, or running supply runs, or in positions away from the front line providing support. Please enlighten me on these subjects.
gpt
The 15 hours statistic is one often-quoted by cynics and borderline heretics.  Guard your mind, guardsman!

In truth, this statistic only applies in certain circumstances.  Against certain xeno species (non-feral Orcs, Tyranids, Eldar, Dark Eldar, Necrons, Tau, etc), and in the case of a major warp incursion (where Traitor Space Marines and/or daemons) are present, it is quite true that a guardsman's life expectancy is quite low (though victory is always assured if one keeps the Emperor foremost in ones mind!).  However, such battles only constitute a small fraction of Imperal Guard operations.  The guard is truly an elite fighting force, when compared to its normal enemies.  

Planets serving traitorous governors gone rogue, epidemics of feral orcs, nascent chaos cults... all these things and more constitute the vast majority of the guard's combat history, and in these cases, both your training and your equipment will let you far outclass your opponent.  Think back to your home planet's PDF forces.  Whether you grew up on a feral world, feudal world, imperial world, hive world, or any other type of system loyal to the Emperor, your planetary PDF was, while properly pious and brave, far inferior to the Emperor's Imperial Guard, and enemies of that quality are going to be your standard foe, guardsman.

So have no fear!  Take your lasrifle in hand, face forward, and boldly stride into battle!  You are the point of the Emperor's sword, the flat of his shield!  You will be victorious!