What is vehicle enhancement?

Enhancement is a way to improve a few stats of your troops before you get to the next tier. You can do this for any troop type but it needs to be unlocked for each type through research. Once unlocked you can enhance the troops (vehicles in this case) with money.

Enhanced T7 troops will be better than T7 but not as good as T8. Something like T7.5. Once enhanced they will also need money to be healded but will heal faster than standard troops.

Once you reach T9 then enhancing is the only way to improve them (so far anyway).