For the US Army the path seems to be for a qualifying soldier to apply to Officer Candidate School from where he or she is commissioned as a junior officer. Warrant Officers may also gain a commission. Since their rank is roughly equivalent to junior officers they may be commissioned with a higher rank, from which comes the term Mustang Officer.
Partly. There are three routes to commissioning in the U.S. Army: ROTC, OCS, and West Point. All three are actually options for active duty and reserve component soldiers.
In Traveller terms, provided the soldier has completed their FIRST term as an adult as a soldier, they can still enter the Service Academy. Otherwise, that door shuts. (I forget if it's under-22 or 23 for eligibility, I enlisted at 26 and was never eligible)
With regard to ROTC, there is the Green to Gold program which allows soldiers to break service and finish school through a school with an ROTC program.
And OCS, which is pretty straight forward.
Every army does it differently based on culture. Smaller armies may identify potential officer candidates earlier and put them through the normal entry path. Armies with significant numbers of Warrant Officers or specific technical requirements may commission to a specified rank with a pay grade that reflects the candidates professional knowledge.
Again, in the U.S. Army (the only one I can speak of with any authority), Warrant Officers actually *ARE* commissioned officers once they are promoted from WO1 to CW2.
The U.S. Army also has the O-1E, O-2E, and O-3E ranks which actually pay more, provided you have been enlisted for a certain amount of time (I forget which), regardless of your method of commissioning.
Professionals (Medical, Lawyers, and Spiritual) enter at a rank based upon their education. J.D.s and Masters of Divinity get you in at the O-2 level, Doctoral degrees at the O-3 level. Sometimes, even higher. We had a battalion surgeon with the 82nd ABN in Iraq who came in as an O-4 because he was an M.D. with 10 years surgical experience.
There are also pay bumps to help bridge the gap between military pay and civilian pay, which can be quite handsome for some of the more specialized fields of medicine.
What does this mean for T5? Well the career resolution system doesn't take account of professional knowledge, age or any other characteristic that may recommend a ranker as an executive leader. T5 uses Soc to determine if you cut it as an officer. I'm still sticking to what I said in my first post but again I'll say if the ref thinks that a CPO or Master Sergeant has served long enough and gained enough professional skill allow the second roll to see if they progress to 1st Lt. or start them as a Captain.
Yeah, I'm not sure how to properly introduce more "realism" into the system without getting too granular. PLUS, the BA and US Army of 2013 bear little resemblance to the armies of 1913 or 1813. Who KNOWS how things would roll in the Imperium.