Forward operating base.
Lightweight firebase modules can be delivered directly to the battlefield by Condor dropships. The modules then unpack and can assemble basic structures and UNSC weapons systems, protected by up to four turret emplacements. Upgrading the firebase to a combat station allows basic infantry to be deployed. While the command center and headquarters expansions make additional units available. Each upgrade also opens additional build locations for support structures.
The Spirit of Fire's expeditionary firebases trade a portion of the original Heron-transported "pod" system's operational flexibility for substantial mass and resource savings. Unlike the older pod firebases, additional pre-manufactured base structures must be transported to the firebase rather than assembled on-site, but this method saves irreplaceable strategic resources aboard the Spirit of Fire. The older pod bases remain in reserve, with the Heron dropships used exclusively for mass deployment of cargo and troops in secured rear areas.