This building creates a shield around your whole base. They are costly and take up one building slot. When the energy is drained, it shuts down, and all the buildings in the base are vulnerable to attack. It takes time for it to regain its energy levels and regenerate the shield. It can endure a direct hit from UNSC Spirit of Fire's Magnetic Accelerator Cannon. Having multiple Shield Generators up at once will increase the strength of your shield.