Bastion is the seventh mission of Ace Combat Zero: The Belkan War.
Days after the Republic of Ustio's liberation from Belkan control, the allied forces obtain intelligence that Belka is developing nuclear ordnance and a weapon of mass destruction, the "V2." In response, the allied command authorizes the deployment of troops at Glatisant, a mountainous region in south Belka, with the goal of checking for the presence of nuclear arms and resource acquisition.
Numerous allied troops storm Glatisant in May 17, among them the 66th Air Force Unit. Cipher and Pixy attack various important locations throughout the area, including anti-air fortifications and a regional command center, causing severe damage to the Belkan forces spread along the mountains. The attack leads to the collapse of the Belkans' first line of defense and the opening of an entry route into Belka for the Allies.
- This mission is the first in Zero to include a return line.