Weapon/Armorsmith.

Weaponsmith and Armorsmith are two features many new players don't understand in the game. All they know is that they upgrade attack or defence of a certain troop. To build a Lv. 1 Armorsmith/Weaponsmith, you'll need a Lv. 3 Drill Ground. After you've built these, you can upgrade the attack of a certain troop in the Weaponsmith and the defence of a certain troop in the Armorsmith.
Every time you upgrade each level in the Armorsmith or weaponsmith, the defence/attack will increase by 1.5%.
For each type of troop, you'll need a different level armorsmith/weaponsmith.
When a troop is upgrading in either the weaponsmith or armorsmith the new stats are not shown, however they've still been upgraded and are there, just not visible.
Weaponsmiths and Armorsmiths only affect the city they're built in, so if you have more than one city, it'll only affect the troops that were made in that city.
When you upgrade the level of a certain troop in either the armorsmith/weaponsmith to a certain Lv., for example, Lv. 20, then all these soldiers of this certain type will be Lv. 20 attack/defence, that means if you demolish the armorsmith/weaponsmith, these troops will still be Lv. 20 in attack/defence and will keep being recruited with Lv. 20 attack/defence.

Koramgame help: Here is an example of Qing Calv. Details and how they are used and levelled up.