In the Weapon Lab you can create powerful prototype defense structures that will help to shield your base from the evil Blackguard.
They are in an experimental state though which means that after 7 days they become unstable and self-destruct.
So if you come to your home base and your Prototype Weapon is gone – it most likely had a loose screw and blew up. You can see for how long your Prototype will be active by tapping on it.