Istas Fortress was an Independent State Allied Forces facility located in the tropical region on the southernmost peninsula of Usea, southeast of Los Canas. The fortress's airfield and VTOL facilities fell under Erusian control following the ISAF's evacuation to the east, but were reclaimed soon after the ISAF commenced counteroffensive operations on the mainland.
The Istas Fortress complex was comprised of Scion Airbase, located atop a mountain plateau; a Vertical Take-Off and Landing (VTOL) base atop the western mountain peaks; submarine docks, which were constructed under the base of the mountains to the north; and a resupply and refueling depot to the west. Istas Fortress's defensive capabilities were further enhanced by the area's rugged and heavily forested terrain.
As tensions between Erusea and the ISAF erupted into open war, Istas Fortress became an important ISAF installation on the frontlines. The ISAF would use the fortress facilities to support its western operations in San Salvacion. When the Erusians began using the Stonehenge Turret Network as an anti-aircraft weapon, however, the resulting lost of air power put ISAF on the defensive, and Erusea proceeded to launch a massive attack on the fortress. Outnumbered and outmatched, the ISAF retreated and abandoned Istas Fortress, and the facility quickly fell under Erusian control.
When ISAF commenced its counteroffensive on the mainland, Istas Fortress became a prime target. If the fortress could be taken, the Erusians' defensive line to the north—the "Tango Line"—could be flanked and rendered useless. On February 28, 2005, ISAF squadrons were sent on a dangerous mission inside Stonehenge's effective range to cripple the fortress. During the operation, Stonehenge opened fire, launching several volleys at the ISAF aircraft, which managed to avoid destruction by reducing their altitudes to below 2,000 feet. Despite Stonehenge's efforts, Istas Fortress was reclaimed by ISAF, and the Tango Line collapsed. ISAF would use this opportunity to advance on Los Canas to the north and liberate the city.