Based on rapid-deploy fortifications in the War Games training simulations set up by Isabel, these bases are vitally important objectives that define the win conditions of the Strongholds training mode. Each Stronghold has infantry, air, and vehicle support structures already attached. Each captured Stronghold increased population capacity.
The concept of Strongholds began in War Games, but Isabel continues to run optimization routines on the design templates she uploaded to the Spirit of Fire's databanks. Isabel has gleaned many novel upgrades from the logs kept by the ship's previous AI, Serina, of the many prior engagements of the Spirit of Fire.