You can create defensive towers at the Cyber Plant. Each type of tower has two parameters: armor and damage.
Rocket Tower is the basic tower with 560 armor and 68 damage. You can build one Rocket Tower for 2,400 metal. Bonus damage:
Lightweight Fighter: +200%
Heavy Fighter: +150%
Battleship: +150%

One Laser Tower has 2,240 armor and 263 damage and can be built for 7,200 metal, 800 polymers, and 200 antimatter. Bonus damage:
Heavy Fighter: +200%
Cruiser: +150%
Dreadnought: +150%

One Gauss Tower has 11,200 armor and 1,106 damage and can be built for 28,000 metal, 6,000 polymers, and 2,000 antimatter. Bonus damage:
Cruiser: +200%
Battleship: +150%
Bomber: +150%

One Ion Tower has 28,000 armor and 2,766 damage and can be built for 50,000 metal, 20,000 polymers, and 7,500 antimatter. Bonus damage:
Battleship: +200%
Dreadnought: +150%
Destroyer: +150%

One Plasma Tower has 25,000 armor and 4,500 damage and can be built for 20,000 metal, 15,000 polymers, and 12,500 antimatter. Bonus damage:
Destroyer: +200%
Bomber: +150%
Titan: +150%