Tools for the troops in battle?

Ive got a great idea. You could have another type of troop/spell/tool for attacking. Basically it is like a barrack that could make machines. Like troops only its FOR troops. Things like a wall smasher that houses 7-14 troops and travels towards the wall until it gets destroyed or hits the wall. When destroyed, it spawns the troops in it!

Carrier balloon: When shot down, spawns a bunch of ground troops.
Armour: Troops walk in with temporary armour but MUCH lowered speed. ITS TEMPORARY!
Drill: Gets where you tap it through drilling. (Only 2 by 2 space needed.
Only for higher level gameplay

Other suggestions for the tool maker/Barracks?