Agent Ranks (Apocalypse)

Promotion Eligibility:

Rank           Prerequisite
Rookie         None
Squaddie       Must earn over 8 combat rating points
Squad Leader   (Rookies + Squaddies) / (Squad Leaders + 1) is more than 4
Sergeant       Squad leaders / (Sergeant + 1) is more than 3
Captain        Sergeants / (Captains + 1) is more than 2
Colonel        Captains / (Colonels + 1) is more than 1
Commander      No commander, and more than one Colonel

Up to five units may be promoted after any given mission. The units with the highest combat rating are selected for promotion.

In effect, this means that you need to hire:

• 5 soldiers to get 1 squad leader +4 Squaddies/Rookies
• 15 soldiers to get 1 sergeant + 3 squad leaders +11 Squaddies/Rookies
• 45 soldiers to get 1 captain + 3 sergeants + 9 squad leaders + 32 Squaddies/Rookies
• 90 soldiers to get 1 colonel + 2 captains + 6 sergeants + 18 squad leaders + 63 Squaddies/Rookies
• 135 soldiers to get 1 commander + 2 colonel + 3 captain + 9 sergeants + 27 squad leaders + 93 Squaddies/Rookies

Apparently it is impossible to hire 130 in Apocalypse and thus you cannot get a commander.