Ok, to put things into less confussing terms, military ranks are a function of three different variables: Pecking order (seniority), Functions and overall Men-under-your-charge.
In fact the easiest way to address military ranks is by watching party sizes.
The smallest military unit possible is the squad or team, and thus the
team leader is one of the lowest ranks with some authority, the exact name varies depending on the nature of the army, but the most common is Corporal. Now even on a small unit a second in command comes in handy, someone to protect, assist, provide advice and if needed replace the team leader on a temporal basis, thus the
second in command ensues (the vice corporal, lancer, lancecorporal, etc). Below the second in command, lay the
specialists, soldiers who while not being in charge, hold an opinion that is very valuable to the team leader. Then there is an obvious difference between the
professional soldiers,
the rookies and the
voluntaries that fight alongside them, but who ultimately only follow orders, lacking the real trainning and experience the professionals hold.
Then a group of teams make a platoon or centuria, which is commanded by a
Junior Officer, for example a Centurion, this man's job is to coordinate all team leaders, but not being one himself, he is there to call orders, of course given the logistics of coordinating a group of teams, he needs an
Assistant.
A group of platoons forms a company, a Company is directed by a
Captain (The one at the head) who is assisted by a special Junior Officer who works as his second in command, this person is the
Lieutenant, and given the logistics needed to coordinate this amount of people there is also an
Ensign(or sub lieutenant), someone who relies orders from the Captain and the Lieutenant to other Officers.
At this point confusion starts to ensue, as there is a high variation of groupings and they vary according to army size. So in short (remember those are descriptions or achetypes, feel free to rename them on your world)
- The voluntary/draftee. Someone with only the most basic trainning at best. Not a real soldier.
- The Rookie. Has been trained but lacks experience
- The Professional. Has both trainning and some experience
- The Specialist. Serves a special purpose on the squad
- The Lancer. Has experience and assists the leader, normally a dead-end rankwise, since someone competent has to remain at this level to ensure the bases are covered.
- The leader. Leads the Squad, most leaders weren't Lancers first, if a leader is promoted or killed, his position will be taken by an specialist or a professional, the lancer is there to make sure a new leader performs as needed.
- The Assistant. He is senior to all leaders, but most commonly only relies orders from the junior Officer
- The Junior officer. He is the head of the platoon.
- The Ensign. A special Junior Officer with no platoon of his own, but who helps to rely the orders from the Captian and Lieutenant
- The Lieuttenant. He is also a junior Officer, commanding a platoon of his own, but also acts as a second in command of the whole company
- The Captain.The head of the company. And if the whole army is only a single company he is also the supreme leader of the army
Higher rankings according to army size:
The Whole army is a group of companies. The army is lead by a
General/Admiral, who in turn is the most senior of the captains
Companies form Battallions, the whole army is a small group of battallions. Each Battallion is lead by a
Commander, with a
Junior Commander as his second in command. The
General/Admiral is the supreme leader and is senior to all Commanders
Companies form Battalions, and battallions form brigades. The whole army is a small group of Brigades. Each battallion is lead by a
Junior commander, each brigade is directed by a
Brigadier General with a
Commander as his second in command. The
General/Admiral is the most senior Brigadier
And since I'm starting to get tired, and fantasy armies aren't likely to get that big (when a brigadier enters the picture we are talking about 10,000 to 20,000 soldiers). The ranks as army size start to increase is: Brigadier -> Major General -> Lieutenat General -> General -> Marshal -> Greatmarshal->Supreme Commander, as the groupings start to get bigger and bigger.