In general, an officer is a soldier who has authority over other soldiers. In modern militaries, a commissioned officer is an officer who is formally granted that authority by a government.
This document granting such authority is called a commission, as in the officer is literally commissioned by the government to lead. A non commissioned officer is an officer who was not expressly commissioned, but has been promoted to the office.
What this means is that commissioned officers are, usually, trained at an academy, commissioned, then assigned a duty. These officers are generally trained for leadership or specific roles *before* they do them. Non commissioned officers enlist, are assigned a duty, then promoted to leadership as they prove competency/gain seniority.
Commissioned officers are the “educated” academy folks, the ones who are trained to lead, command, or perform specialized jobs such as fly a fighter plane, or command a platoon of tanks. Non commissioned officers are from the common soldiers, the enlisted troops. They start at the bottom, they do the “grunt work,” are the ones “on the ground,” and make up the bulk of the military.
This is with regards to a modern national military. Older militaries were very different in not just organization, but in their function and purpose.
While not part of the original question, anyone interested should read the other posts regarding warrant officers, another important part of military leadership.
NCOs are sergeants (or petty officers or whatever). They are enlisted personnel who have lots of experience. This is in contrast to officers, who in most militaries join directly as officers after having undergone some sort of advanced training.
NCOs are important in that they can basically help soldiers learn how to be better soldiers. An officer trying to help an infantryman is like an MBA trying to help a programmer: they can give high-level advice about tactics and motivation and stuff, but can’t give good advice on how to pack things in your backpack for best balance and accessibility in the field, or which field rations taste best, or that the #3 engine needs more oil than the others.
Officers handle the big-picture red-tape stuff and issue orders, while NCOs relay the orders to the troops, supervise, adapt, and accomplish the task in accordance with the commander’s intent.
NCOs are generally much more experienced than officers at ground-level, and are familiar with possible undesirable outcomes for a given plan.
At a company level, it is the unwritten job of the senior NCOs to tell the much more junior officers why their plan is stupid (behind closed doors), and help them amend it in a way that still achieves the intent of the order. The junior NCOs take the finalized plan and direct their men to execute it.
From an episode of *Hornblower:* “The Petty Officer’s job is not to do the task — it’s to see the task is done.”
Watch *Band of Brothers* to see how WWII Army responsibilities and authority developed and were assigned.
Speaking very generally, the Officers are assigned a mission and various resources (people, equipment) to perform that mission. The mission may be to operate a supply depot involving hundreds of people and thousands of tons of stuff. The mission may be to occupy a hill top and hold it against enemy action. Obviously, one Officer cannot do this alone, and has subordinates to complete the many tasks involved.
Here’s where the division occurs — the Officers are concerned with the Goal, the NCOs are concerned with the Method of achieving that goal. A good Officer will give clear goals to the NCOs. The NCOs will train the unit personnel on how to reach that goal — weapons training, medical, cammo, transportation, and more. In turn, the NCO tasks the officer to get the material needed for the training.
Once ready and in the field, now the Officer directs the general situation (take that hill) and specifies methods (tactics) to be used (flanking, mortar fire, coordination with other units). The NCOs then act with their teams to carry out the overall plan. The NCOs are on the front line and can react to local situations. The Officers are a bit further back, seeing a wider view (enemy approaching our left flank!) and give orders accordingly.
You trust your NCOs to lead you through situations you can handle (training, resources). You trust your Officers to put you in situations that are worthwhile to risk your life (tactics serving a strategy).
The US bases everything off small unit leadership. We get a task from officers and we carry out those task in the way we see fit.
Many nations don’t utilize an NCO corps Because their training is more abput listening to direct order vs figure it out as you go.
Every NCO in the US is essentially a Cpt. Jack Sparrow.