The Light Turret is a Turret that is available in Tech Level 2. It costs 25 Carbon and 125 Ore, and is the basic defensive structure for all civilizations. In Tech Level 3, it can be upgraded to the Medium Turret at the Research Center for 100 Carbon and 250 Ore.
Workers and Troopers can also garrison inside Turrets, increasing their attack strength. Turrets are a good way to protect the player's base from raiding parties, but are easily knocked down by any siege units (like the Pummel and Cannon). Note that Light Turrets can only attack ground units - for aircraft, the player should build an Anti-Air Turret.
"This defensive Turret becomes available at Tech Level 2, and once erected, will automatically fire on any enemy ground units or structures within range. In addition, workers, Troopers and some other foot units may garrison themselves within these Turrets for protection, and to lend more firepower."