Quite possibly the simplest of all side missions. Simple make sure your team contains at least two Technician classes. These include the Combat Engineer, Technician, Demolition, and Forward Observer. Then have them proceed to the Armory and stand on the hexes. Doing so will set the Sentry Guns around Apollo to active combat status. They become allied and will try to kill any hostile in range.
This mission can be activated at any time assuming the team possesses the necessary classes. But, it is up to the discretion of the players. The Auto-Turrets will steal large amounts of experience from early hordes, potentially under-leveling a team. It should also be noted that on the Apollo Security Team Campaign Nazara and HAL will hack all the Sentry Guns after their battle, turning them hostile.
This mission is not active in Survival Mode.