During the End War, they attempted to defend the facility when it was attacked by the Tal'darim Death Fleet. Most of the cannons were destroyed by their mothership's phase displacement beam during the attack.
The Glacius plasma cannons are non-controllable cannons the appear in the mission "Forbidden Weapon." While they are targetable, they serve no direct purpose and have no attack, and will only fire at the sky. All targetable cannons are in the path of the phase displacement beam, and are destroyed on contact.