Age of Origins Manage Troops (Troop Promotion)

This is one of a building in the Age of Origins Buildings page.

First thing to note is that the strongest commander recruit event only counts for recruited units, not promoted units: do not waste your speeds here! 

A good strategy is to always keep this active with your recruit buildings. For example, you can have a level 13 factory recruiting t5 cannons and a level 19 factory recruiting t7 cannons and then you can promote your t5 to t7. You can promote more than you recruit, but it is a set limit. You will eventually run out of things to promote as you build all of your recruit buildings to maximum levels. 

I like to promote my sniper/cannon/emp/shredder first when I unlock the next tier troop and then continue upgrading from the lowest first: promote your t1 infantry to t3 before you promote your t3 to t5.