Defenses

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 that 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.

Note: After a battle, 70% of destroyed defensive structures are automatically rebuilt immediately without additional costs, unless destroyed by an Interplanetary Missile (see Combat).

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.

Pros

A good defense provides a degree of protection, allowing you to build up your resources and fleet.
After combat, 70% of destroyed defensive structures are automatically rebuilt for free.
Defense has NO effect on the number of developed fields on any planet.
Defenses generally are much more powerful than ships for the same amount of resources spent, not counting Rapid-Fire.
Defenses allow you to spend less time in the game, while still maintaining a competitive economical growth rate. In other words, Turtles are able to pursue a more relaxed style of gameplay.
Defenses can’t NORMALLY be turned into debris fields (DF) unless playing in a special tournament or in a universe that has special rules allowing “Defense into Debris”. This means that there is no incentive for an attacker to try to blow up your defenses in combat, because they will not generate debris for the attacker to recycle.

Cons

Successive waves of attacks can erode defenses into insignificance. There is therefore a constant need to build enough defenses to keep other players’ increasing fleets from breaking through your defense.
Once built, defenses do not contribute to your economy in any way. They don’t bring in resources, and they don’t enable you to raid other planets for resources or crash other players fleets.
When your defenses are destroyed during an attack, you lose points and the resources you put into building them.
Interplanetary Missiles (IPMs) targeted at specific parts of your defense can quickly leave you vulnerable to attack. To remain effective, large defense arrays requires the added expense of Missile Silos and Anti-ballistic Missiles (ABMs) to protect them.
A determined player or group of players can completely obliterate even a massive defense with large volleys of Interplanetary Missiles, resulting in huge point losses for the target player.