Bunker Invictus
This is potentially the site of Mega Mind. We do not know what Mega Mind is, all we have is a written reference on an old map.
Soldiers at or around the time of the Fall led by Capt. Johnstone of the Parachute Regiment pushed into Bunker Invictus in an effort to use it to house the remnants of the British Army, with civilians being killed to make space for them. These soldiers used plain clothes troops to deceive the civilians. It is likely that Invictus was a highly militarised society as a result.