- This article is about an in-universe event. For the in-game mission, see Siege of Farbanti.
- "An end to the war would be a nice birthday gift as well."
- ― AWACS SkyEye to Mobius 1
Operation Autumn Thunder, also referred to as the Siege of Farbanti, was one of the final operations launched by the ISAF as part of the Continental War. Its objective was to besiege the Erusean capital and capture the military GHQ in order to force Erusea's unconditional surrender and prevent the completion of Megalith. 
Following the fall of Erusea's final line of defense in Whiskey Corridor, the Erusean forces retreated to reinforce their capital. Rather than concede defeat, Erusea's military planned to make one last stand in an attempt to stave off the Allies long enough to complete Megalith. If the ISAF wanted to prevent the completion of this new Erusean superweapon, it would have to eliminate the Eruseans' unrelenting opposition and bring the war to an end.
To ensure the mission's success, the ISAF deployed its ground, naval and air forces in a coordinated effort to besiege the Erusean capital. ISAF naval guns bombarded the Erusean defensive positions while amphibious landing forces stormed Farbanti's flooded municipal district to the southwest. Simultaneously, ISAF tank battalions entered the city via Silver Bridge to the east. In addition, the ISAF's preliminary reconnaissance of the capital had revealed a large tank force inbound from the north of the city.
ISAF fighters, including the now renowned ace Mobius 1, provided close air support for the ground forces, which were pinned down by intense crossfire and artillery shelling from the Erusean defenders. During the engagement, Mobius 1 successfully sank the remaining Erusean naval forces positioned around the capital's waterways and destroyed Johnson Memorial Bridge, thereby cutting off the Erusean reinforcements' most direct route into the city. Gradually, the city's resistance began to crumble, and the ISAF ground forces advanced toward the Erusean GHQ. As the battle turned in the Allies' favor, AWACS SkyEye detected several helicopters taking off from the Erusean GHQ (most likely carrying Erusea's high-ranking command personnel). However, ISAF fighters quickly downed the choppers before they could escape the capital, effectively crippling the Erusean military hierarchy.
Shortly after the helicopters had been eliminated, the fearsome Yellow Squadron entered the airspace and attempted regain air superiority over Farbanti. Recognizing the danger posed by the Yellows, SkyEye ordered Mobius 1 to engage the Erusean aces. After a long, ferocious dogfight, Mobius 1 shot down all of the Yellow fighters, including their leader, Yellow 13. With the skies clear of enemy fighters, ISAF ground forces captured the Erusean GHQ and broadcast orders for Erusea's immediate surrender.
The operation was an overwhelming success for the ISAF: many of Erusea's top military leaders had been killed in action, including the Supreme Commander, and Erusea's remaining military forces had been summarily crushed. Erusea officially capitulated at noon on September 19, 2005, bringing about the war's official end. Overall, the ISAF's victory had come at an extremely high cost in casualties.
- In the mission debriefing, Erusea is said to have accepted the terms of surrender at 1200hrs; this is more than six hours before the operation's start time, 1820hrs, which is stated on the pre-mission titlecard.
- Operation Autumn Thunder takes place one year to the day after the ISAF's successful defense of North Point during Operation Umbrella.