It's an item provides you with specific protection for your base as well as increase attributes for base protections such as Guardian Protector, Protector - Kirov Airship, Boeing AH-64 Apache, etc.

To activate it, you can click on your base on the world map then on the “Protect the Base” button. You will find a “Switch skin” icon at the upper right of the screen, click on it, then choose the skin you want to activate and click on the activation icon. You can also click on Iron Blood Relic and click the button “skins,” and choose the “Base protection skin” tab, where you will find all the protection skins in one place. You can use the skin protection according to what is available.