Pretty much every human character we see in 40K is some kind of soldier (those who aren't are supporting the soldiers). But what seems to have been ignored in a lot of 40K literature is what the career of an average soldier / officer looks like.
In real life, Enlisted Men or Officers move up the rank based on a system:
http://usmilitary.about.com/cs/armyprom ... ions_5.htm
http://usmilitary.about.com/od/promotio ... erprom.htm
But in the setting we generally don't see any kind of system. I'm not just talking about how 40K has a million worlds and a million different promotion systems, but the fact that we haven't even seen the promotion system for even one of the well-known regiments - like say the Cadians.
Hence, one of my objectives for fanfic writing will be to create a military career system for the regiment I feature in my stories (The Brennus Mechanized, mentioned in a few of the previous threads). To review, this "regiment" is a mechanized force that combines 300 armored vehicles with 4,500 men - essentially providing the "Armored Fist" squad support for other regiments as noted in the fluff (or the "Mech" lists on the tabletop).
This career system will also be used by the Brennus Planetary Defense Force (The "Army", to differentiate vs the Imperial Guard).
So, to start with, I'm thinking of the following points:
1) Unlike the US military, Brennus has a conscription system. This is 40K and Grim Dark, but there's also a practical reason - the northern portion of the planet is still home to a substantial Orkish population, and a constant low-intensity war is being fought against them.
Out of the 90,000 men in the army (out of a population of 10 million), as many as 500 are killed annually fighting the Orks. However, the full army is rarely deployed in the Northern Wastes - typically only half (the "Actives") are in the north, while the remainder (the "Inactives") are far from the frontlines and engaged in rest / refit; alternating between six month cycles out of every year.
Every Brennic male citizen must serve in the PDF for two years minimum (albeit not necessarily in combat roles) starting at the age of 18. Women may volunteer for service and have their own single-gender units.
After their service, troopers remain in the "Fyrd" (their fancy term for Reserves) and may be called up for service in times of crisis. Citizens who are part of the Fyrd are required to attend semi-annual "refresher" training, similar to the US National Guard.
Additionally, when the world is required to raise an Imperial Guard regiment, troopers from both the Army and Fyrd are selected by a combination of volunteering or balloting (men selected by ballot can have someone else take their place). Men selected for Imperial Guard service are expected to remain off-world for service for a minimum of ten years; albeit in practice they are never expected to return.
2) Like the present-day US military, there will be a line between enlisted men (including NCOs) and commissioned officers.
Enlisted soldiers are generally all conscripts, released from service after their second year. The only exceptions are the Huskarls - who are enlisted men who have volunteered for additional three-year terms and who have passed a rigorous physical selection process. Huskarls serve as heavy infantry in the army, and the very best are assigned as bodyguards for high-ranking officers.
NCOs are a combination of conscripts and long-service professionals. Conscripts with potential are sent to a short NCO school, and those who perform well after their term of service are offered permanent NCO positions. Professional NCOs then advance in rank similar to US Army NCOs - climbing up various NCO ranks from Sergeant, to Staff Sergeant, to Master Sergeant. It is also possible for NCOs to earn a commission via merit or attending Officer School.
Commissioned Officers are all professionals, selected from each year's batch of conscripts based on their mental proficiency scores (the Brennus Army wants thinking officers). Those who are selected and who accept must undergo a four-year training course, which combines both classroom and field training (including combat). They get the rank of Brevet Lieutenants halfway through the course, and are promoted to full Lieutenants (leading platoon-sized units called "Troops") at the end of the course (at the age of 22).
After this, the career of an officer can take one of two possible paths - the "Line" path, and the "Knight" path.
"Line" Officers focus on one specific combat arm / support service. However, Line officers are barred from achieving the highest ranks, and their progression from Lieutenant is as follows:
- First Lieutenant (leads company-sized units called "Lances") - generally reached after three years as a Lieutenant
- Captain (Leads battalion-sized units called "Squadrons") - generally reached after five years as a First Lieutenant
- Grand Captain (leads multiple battalions called "Orders") - generally reached after five years as a Captain. This is the highest available rank for a Line officer.
Meanwhile, "Knight" officers are those who have served in at least three different arms, the logic being that the Brennus Army emhasizes in combined arms. This is a much more difficult path and few officers take it, but only "Knight" officers can reach the highest available ranks. Their progression is as follows:
- Knight-Lieutenant (leads company-sized units called "Lances") - achieved after a minimum of three years, averaging five or more. The officer must have served in at least three different arms (usually infantry, armor, and artillery) to qualify.
- Captain (Leads battalion-sized units, called "Squadrons") - generally reached after five years as a Knight-Lieutenant
- Major (leads multiple battalions, called "Orders") - generally reached after five years as a Captain.
- Colonel (leads a Division-equivalent, called "Division" in the Army and "Regiment" in the Imperial Guard ) - generally reached after seven years as a Major, and the highest "assured" rank for a career officer. There are always just ten Colonels - nine for each of the nine Divisions in the Army, and one Colonel of the Imperial Guard Regiment.
- General (leads multiple Divisions) - selected out of the available Colonels to command an entire military district.
(Note: And yes, I know the unit names are awkward. They are also not final. But it's a reflection of the fact that much of the world was living in D&D-style Medieval conditions just two generations before getting mechanized armies, if anyone has suggestions feel free to give them

Officers who wish to retire (even at a relatively young age - e.g. Knight Lieutenants) are allowed to do so but automatically become Reserve Officers for the Fyrd, where they continue to earn a fraction of their regular pay based on rank achieved and years of service (as a form of semi-pension).
Obviously, an exception for both enlisted ranks and commissioned officers are for those selected to become Imperial Guard - both are considered to have opted for the ten-year term of service.
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I'm also thinking of creating a special subset of the officers similar to the Prussian General Staff model, wherein exceptionally talented officers (regardless of rank) are given special staff training.
But I think that's already a ton of details and some people (e.g. Skimmer) may already be shaking their heads at some of the ideas I put here
