The Base is your command structure you start with on each mission, the goal being to protect it at all costs. During each mission Titans will approach it with the intentions of destroying it from one or multiple directions. The base itself is tough but it must be defended to survive any level.
The base does have limited sheilds, these sheilds can protect it for a few hits from the titans (killing or damaging a Titan each time), The base has 40 HP, a swing from a titan usually doing from 4 to 6 damage. For every 10% of its HP intact you will gain $100 at the end of the level. But the Repair Drone and the Repair powerup can repair it and generate some income this way. The supersheild can be used to also defend it against non bosses for a short while.
The base has no defensive wepons to speak of. Other than its defensive sheilds. So it need to be defended by the player. This is done by placing structures, such as Blasters, Refineries , Mines , ect... It is also unaffected by Add-On buildings, and stealth. The only building that affect it is the Shield Generator.