Need help with military units for my novel . [ OT ]

I would employ the term'Legion' for the armies of heaven and hell; this was the basic unit of military organization in the Roman Empire, when the Catholic Church developed and expanded. Could supply a more refutable reference if I wanted; but here's Wikipedia: http: //en.wikipedia.org/wiki/Roman_legion 
 
 This shows the breakdown of unit hierarchy in most modern militaries: http: //en.wikipedia.org/wiki/Military_organization 
 
 Types of military units typically include Infantry, Mechanized Infantry, Armored Cavalry, Armor, Airborne, and Artillery. Though only infantry, armor and sometimes cavalry are organized at the division level. These will be organized in a similar fashion no matter what nation they are from, the difference generally being unit titles. 
 
 For example, American unit names are typically pretty straight forward; 1st Infantry Division, 1st Armored Division, 11th Armored Cavalry Regiment, 75th Ranger Regiment, etc. While units are often deployed in divisions, each brigade or regiment may function very independently. 
 
 Russian infantry units are often organized at the Brigade rather than division level, so you are more likely to see something like the 131st Motor Rifle Brigade, rather than a full division. Sometimes these units will also have more formal ceremonial titles ( Russian Ground Forces are fond of using the title'Guard' ) for example the 138th Guards Motor Rifle Brigade is an active Russian infantry unit. Sometimes Russian units will sport more specialized names directly related to their equipment however; examples would include the 130th Machine-Gun Artillery Division and the 719th Multiple Rocket Launcher Regiment. 
 
 It's also important to consider that in modern armies, even infantry units are equipped with armored vehicles for transportation, including IFVs like the M2 Bradley and BMP-3, which are capable of fighting tanks.
