I have an idea.
How about, instead of just officers, every soldier can become a force commander.
What I mean to say is, none of this commission 'I went to college' bull. In a real war, you don't need paper, you need experienced leaders and those who know how to command.
So, we have only a few, maybe ten ranks. You gain ranks based on time served. Time deployed is worth twice as much as time not deployed, to favor field experience. However, rank is only a symbol of experience, and determines your paygrade.
Higher ranked guys are not automatically superior in the chain of command. They are just better paid, and have spent more time in the service or in the field, than their lower ranked counterparts.
Officers are not those who hold a 'rank,' but the ranks who hold an office. An officer is a soldier who has training or experience enough to be certified to serve an office, such as a company commander, or even a general officer. There are no 'commisions,' but certifications.
You can be certified to command a company, but not be in command of a company if you are not needed.
Training for officer positions is of course given as the soldier wishes to advance. "Hey Boss, I want to take Platoon Leader Training."
So instead of having their rank changed, they remain the same rank, but now become eligible to fill an officer position on completion of their training.
"Oh look, our commander has died/been reassigned, what do we do!?"
"Don't worry, just appoint the next available guy with the most months of experience and highest command certification!"
Very useful for sorting out chain of command issues on every level during even the most ****stormy of situations, because it's so simple.