The only fortress variant that contains a Detector Tower within.
It's not necessary to destroy the Detector Tower for the game to consider the fortress destroyed.
Visually: Detector Tower.
On the map: Oblong perimeter - same as Crane and Bunker Hell. 4 large radar signatures lined up on one side.
There is a unique and ominous banner post filled with skulls in the lower part of the base.
Also, of course one does not simply walk into Mordor...
Strategy possible as of Patch 1.001.102.
I throw an Orbital Laser to destroy 3 fabricators and then use Eruptor on one more for extra reliability (the Orbital Laser can get distracted by hulks or dropships).
I use the Commando the last two and GTFO.
This is an example of a non speedrunner solo clear.
Zovc for the map layout.
Clark for annotations.