Defenses are structures built to protect your planet during Combat. As they’re attached to the surface of the planet (or moon), defensive structures are not mobile or removable by fleets, so you can’t use them to raid.
There are three types of defensive units: Turrets, Shield Domes, and Missiles.
Turrets are cannons which fire projectiles, lasers or other types of energy discharges to shoot at attacking ships. They usually have low armor and shielding, though some have higher structural integrity than others.
Shield Domes provide greater endurance during attacks, because they can absorb much more damage and give extra time for turrets and defensive fleets to shoot back.
Missiles can be used to attack enemy planetary defenses (but not ships), and they can also be used to defend from incoming missiles.
The base time required to construct a defensive unit depends on the amount of metal and crystal the unit costs (more expensive units take longer to construct). Unlike other structures, defenses never increase in cost. Construction times may be reduced by Shipyards and Nanite Factories.
Unlike buildings, it is not possible to cancel the production of a defensive unit. Once resources are put into building a defense, those resources can never be retrieved. You can only build defensive structures one at a time, but can add an unlimited number of defenses to the build queue. Unlike buildings, defenses don’t take up any fields. This means you can build as many defenses as you please, provided you have the necessary resources.
The Rocket Launcher (“RL”) is a simple, cost-effective defensive unit. Operating on the same principle as common ballistic firearms and requiring no further research, its low manufacturing costs make it effective against small fleets. In the early game they are used to deter overnight raids by weaker players. In massive numbers, they can be a deterrent even to larger fleets, making an attack unprofitable. They are also used as a fodder unit to protect bigger, more expensive defenses.
Note: For pros and cons of defensive structures, see Defenses > Defense Comparison
The Light Laser is the next defensive structure that most players will build. It’s used as fodder at all stages of the game, much like the Rocket Launcher, but is better in two ways. Light Lasers have a higher shield and attack strength than Rocket Launchers, and Cruisers do not have Rapid-Fire against Light Lasers (100 Light Lasers are usually enough to repel 20 Cruisers, while 100 Rocket Launchers will usually be demolished by 20 Cruisers because of Rapid-Fire).
The Light Laser costs crystal in addition to metal, making it 25% more expensive. It is also weak against Destroyers, while the Heavy Laser and Ion Cannon are not. Thus, due to their ‘balanced’ cost between Metal and Crystal, building Light Lasers is the best way to deploy a large amount of firepower and ‘fodder units’.
Note: For pros and cons of defensive structures, see Defenses > Defense Comparison
The Heavy Laser (“HL”) is an improvement in sheer power over the Light Laser. Destroyers do not have Rapid-Fire against it and that fact alone may make it better fodder than Light Lasers in certain cases. Large numbers of Heavy Lasers may force your opponents to use Bombers, which have less firepower than Destroyers and are not effective in fleet-against-fleet combat.
Note: For pros and cons of defensive structures, see Defenses > Defense Comparison
The Ion Cannon is a defensive structure with a relatively high shield power. It fires a focused beam of ions capable of obliterating any unshielded electrical system and destabilizing the shield circuits within its target. These combined effects often cause the destruction of the targeted ship.
It can be useful to build as fodder when you have excess crystal, as it is the only defense which costs more crystal than metal. Another reason to build Ion Cannons is because only the Bomber and the Deathstar have Rapid-Fire against it. This makes them useful when defending against fleets of Cruisers and Destroyers that would rip apart your Rocket Launchers and Light Lasers.
Also note that the Ion Cannon can absorb up to 500 damage per round which is the highest shield power of any turret (only the Shield Domes have more). This makes it very useful against a Cruiser or Heavy Fighter fleet since most of the attacks will be deflected by the shields, while anything with Battleship strength will easily rip through the shields. Despite this, Ion Cannons are very useful defenses even in small numbers as they will draw and absorb a large amount of damage per round.
The Gauss Cannon is a “rail gun”, a system of powerful electromagnets which fire high-density metal projectiles at extremely high velocity by accelerating them between a number of metal rails. It is often compared to the Plasma Turret as an attractive endgame defense, having more shield power per resource, and comparable weapon power. It deals noticeably less damage per round to powerful capital ships, but is more effective than Plasma Turrets at taking out lesser ships, because you can build more of them. The Gauss Cannon is capable of bypassing the shields and the hull of both Small and Large Cargos, Fighters and Cruisers, destroying them with a single shot. This means a large number of Gauss Cannons are capable of wiping away a large amount of fodder spacecraft. A small number of Gauss Cannons with a large amount of fodder will generally prevent any number of Cruiser-based fleets from attacking. Gauss Cannons become less attractive against more advanced opponents, as Deathstars have Rapid-Fire against them, whereas nothing has Rapid-Fire against Plasma Turrets.
The Plasma Turret is the most powerful defensive unit in the game. It is fairly expensive, but well worth its price. It uses a powerful electromagnetic accelerator to fire a pulse of superheated, compressed gas, or plasma, at an extremely high rate of speed. There is no ship with Rapid-Fire against the Plasma Turret. Plasma Turrets are also useful for being able to destroy the widely-used Battleship in as little as one hit, deterring attacks from fleets containing them. One-on-one, a Plasma Turret is significantly stronger than a Battleship: at base stats it has 3,000 attack, 300 shield and 10,000 armor, against the Battleship’s 1,000 attack, 200 shield and 6,000 armor. How many hits a kill actually takes depends on both sides’ Weapons, Shielding and Armor Technology levels, and on the chance a damaged unit explodes at the end of each round: one hit is often enough, but it can take 3 or more if the techs are very one-sided. It takes roughly 35-40 of them to destroy one Deathstar, but it would take proportionally more Gauss Cannons, because each time the Gauss fires it has to go through the Deathstar’s shields again, while Plasma fire is more concentrated in fewer turrets. Therefore, mass numbers of Plasma Turrets are really the only effective defense against Deathstars. It should never stand alone in a defense system, but should be backed up with other smaller defenses. The Plasma Turret is capable of bypassing the shields and the hull of any ship equal to or smaller than a Cruiser, destroying them with a single shot. This means large quantities of Plasma Turrets are capable of wiping away a large amount of Cruisers, discouraging the use of these ships to Rapid-Fire your Rocket Launchers. They are better when accompanied by Gauss Cannons (to kill enemy fodder) and large amounts of defensive fodder like Rocket Launchers and Light Lasers (to absorb damage).
Large numbers of Plasma Turrets are also the only effective deterrent against a large-scale attack with Interplanetary Missiles (IPMs). While any determined attacker can “nuke” a defense away, the cost of building enough IPMs to destroy 3000 Plasma Turrets is generally not worth it unless the target has left a huge amount of resources on the planet.
The Small Shield Dome is a defensive structure to use as fodder and give a higher chance of a draw. Only one small and one large shield dome can exist on each planet. Despite their description, and being called a “dome”, domes do not offer any sort of overarching defensive ability. They act as a single unit of fodder. Because no ship has Rapid-Fire against a Small Shield Dome, the presence of a pair of shield domes serves as a “block” against Rapid-Fire during a single combat round from Rapid-Fire-heavy fleets (Deathstars or Bombers). The shield increases the chance of draws occurring if the attacker uses a small attack force, such as light fighters. A small dome is invulnerable to the fire of cargos, making it a perfect defense to prevent a planet from being easily farmed. Just remember a small escort of light fighters may destroy the small dome.
The Large Shield Dome is a stronger version of the Small Shield Dome. It costs 5 times the resources and has 5 times the Shield Power. Only one Large Shield Dome and one Small Shield Dome may be built on a planet. Despite their description, and being called a “dome”, domes do not offer any sort of overarching defensive ability. They act as a single unit of fodder.
Some would argue that this makes them not very effective, and that the resources should rather be spent on a Plasma Turret. However, this is not entirely true. Unlike other defenses used as fodder, no ship has Rapid-Fire against a shield dome. The Large Shield Dome usually prolongs the combat another round, many times being the last object that all the attacking ships target. This could yield the difference between a draw and a defeat for the defender, and thus save the defender’s resources from plunder. If a planet is frequently attacked by Rapid-Fire-heavy fleets (Deathstars or Bombers), the presence of a pair of shield domes serves as a “block” against Rapid-Fire during that combat round.
It takes ships stronger than Light Fighters to damage a Large Shield Dome. Light Fighters are not able to penetrate a Large Shield Dome unless the attacker’s Weapons Technology level is at least 10 levels higher than twice the defender’s Shielding Technology level. In practice this doesn’t ever happen, thus a Large Shield Dome will never be destroyed if attacked with a fleet of pure Light Fighters.
Anti-Ballistic Missiles (ABMs) are the only way to destroy attacking Interplanetary Missiles (IPMs). Each Anti-Ballistic Missile destroys one incoming Interplanetary Missile.
Anti-Ballistic Missiles are launched automatically whenever an approaching Interplanetary Missile is detected. Otherwise they do not take part in any attacks, thus they cannot be sent on missions or destroyed by an attacking fleet.
You can store 10 Anti-Ballistic Missiles for every Missile Silo Level on your planet (twice the amount of Interplanetary Missiles).
Interplanetary missiles (IPMs) are designed to destroy enemy defenses. Tipped with an anti-matter bomb, they deliver a destructive force so severe that destroyed defenses cannot be repaired. The only way to counter these missiles is with Anti-Ballistic Missiles (ABMs). In an IPM attack, only the attacker’s Weapons Technology level and the defender’s Armor Technology level are used in battle calculations, as IPMs penetrate shields, including Small and Large Shield Domes. Before an IPM can hit the defense itself, all ABMs on the target planet must be destroyed. Each ABM destroys one IPM.
The range (in number of systems) of an IPM is determined by the Impulse Drive level. Each level of Impulse Drive researched increases IPM range. They do not use a fleet slot while flying. However, they do create Activity on the target planet upon hitting, and the defender receives a combat report in his messages.
You can store 5 Interplanetary Missiles for every Missile Silo Level on your planet.
Hint: Interplanetary Missiles cannot target moon defenses.
This is a comparison of the pros and cons of each defense.
The Rocket Launcher is a good, cheap, early game defense. In later stages they’re only worthwhile as fodder, and massive numbers can absorb a staggering amount of enemy fire in a single combat round, allowing heavier defenses more time to do damage to attacking ships. When under attack, excess metal is often dumped into Rocket Launcher production to prevent it from being plundered.
Pros: Cheap, does a better job as fodder than Light Fighters at half the cost.
Cons: Unbalanced cost, supremely weak, Cruiser’s Rapid-Fire (RF) cuts these down like grass.
The Light Laser is a better defense than Rocket Launcher. These are used more than Rocket Launchers because they are more balanced in cost.
Pros: Better firepower and shields than Rocket Launcher, balanced cost.
Cons: Light Lasers are much more susceptible to Destroyer attacks than to Cruiser attacks, as Destroyers have Rapid-Fire against Light Lasers.
The Heavy Laser is “heavier” than the Light Laser, but as for pure firepower, you’re better off buying 4 Light ones. However, advanced players may use them as a pure armor fodder for IPM attacks. With IPMs only counting armor vs weapon power, you can absorb many more IPMs with fewer losses with sufficient armor tech and heavy laser counts. In addition, Destroyers have Rapid-Fire against Light Lasers, thus making Heavy Lasers a worthwhile defense against more developed players.
Pros: One Heavy Laser can take out a Light Fighter in one shot and “can” damage Deathstars if the defender’s Weapons Technology level is 10 or more above the attacker.
Cons: For the firepower they offer, Heavy Lasers are too expensive.
The Ion Cannon exists mainly as fodder due to its high shield strength but is lacking in actual firepower. They are often used for getting rid of spare crystal, especially during an attack.
Pros: High shield power making them very good fodder, and are great against all ships below the Battleship especially Cruisers and Heavy Fighters.
Cons: Not very cost-effective, and costs 3x as much crystal as it does metal.
The Gauss Cannon is the second-best defense out there. With high shield and attack power and generally low price, they can be constructed in large numbers.
Pros: Can destroy a Cruiser in one hit and its attack is equal to that of a Battleship. Gauss Cannons have a very balanced price for the firepower they offer, thus making them highly efficient.
Cons: Like most large defenses, it can be ravaged by large swarms of fighters.
The Plasma Turret is the most powerful defense mechanism in the game. Its firepower and structural integrity are very high, and when encountered in high numbers, Plasma Turrets can be a tough nut to crack.
Pros: Can destroy a Battleship in one hit (it may take 3 or more if the attacker’s techs are far ahead), and around 7 Plasma Turrets can draw with one Deathstar. Massive numbers make IPM attacks unprofitable.
Cons: Expensive and unbalanced cost. Deuterium cost inhibits building large numbers of these.
Hint: Keep about 1-2 Anti-Ballistic Missiles per turret (topping out at 50-70 missiles) as Plasma Turrets are the main reason players attack with Interplanetary Missiles - until they exist in massive numbers.
A common strategy for defense building is to burn all unused resources on a planet before going to bed or leaving the game for an extended period (resources that cannot be “saved” by loading them onto a fleetsave mission, often referred to as “Resource-saving”). Add defenses to the build queue, starting with the maximum number of the most expensive defense possible, then the maximum of the next most expensive defense possible, and so on, ending with the maximum number of Rocket Launchers. This removes any excess resources that might invite attack overnight. Following this strategy every night will rapidly build up a good defense.