|“||Only one Phase Generator remains... Guard it with your life!
- Kane upon destruction of two out of three Phase Generators, Tiberium Wars
Phase generators were used by the Scrin to shield their Threshold Towers from any attack or environmental catastrophe while under construction. Evidenced by GDI and Nod incursions into Red Zones, the aliens operated on a triple redundancy; each Tower had three phase generators protecting it, while only one was needed.
The generators operated by shifting the Thresholds out of sync with the physical world, rendering them invulnerable to any attack. Destroying Scrin reactors in the vicinity did not seem to adversely affect the phase generators, suggesting that they contained an internal power source. The generators would become unnecesssary after the completion of a Threshold; as the structure would remain out of sync following completion. Therefore, to destroy the Towers, it was necessary to first take out the Phase Generators, and then destroy the Towers before they could be brought online.
During the attack on Rome, GDI forces, led by a brilliant commander, were the first to notice the Phase Generators. After a hard fought battle with entrenched Scrin opposition, the three generators were destroyed. The unprotected Tower was now vulnerable, and the Commander was able to eradicate it with the Ion Cannon. This victory served as a model for GDI forces worldwide, and soon, all but one Tower had been eliminated.
Nod forces, who were attempting to capture a Threshold, dug in near what used to be the Mediterranean Coast, while Scrin Foreman Number 371, needing Threshold 19 intact to ensure his escape, defended it from another side. They managed to hold off GDI attacks on the generators long enough for the Tower to be completed, making it invulnerable to human assault. GDI was eventually pushed out of the area. Nod had managed to acquire the key codes to the Towers some time before, and were able to claim it in the name of Kane and later LEGION.