While ships are indispensable for offensive actions, there are defensive structures to allow players to protect their planets from other players. Those are built the same way as ships and are always ready to fight against attacking ships. Depending on how many defenses one builds, one can defend more or less resources, as a big defense makes attacks unprofitable for other players. Though there are also those players who systematically attack heavily-defended planets (so called turtles).


==Balanced buildup==


When building a fleet there are some major points you have to pay attention to. The same goes for defenses. The amount of defensive structures should always be matched with the needs of the planet/moon the defense is built on. If your goal is to just save those resources you produce overnight it would be overkill to build a huge turtle worth some hundred-thousand points.


Though if you want to defend your whole fleet (at least for a while) you need a much bigger defense. The right mixture of the different units is very important too. Similar to small ships, small defensive-units, built in large number, take the role of "Cannon Fodder", while you build the big guns for the big bang.


But no matter how strong your defense is and how well thought-out its design, the best defense is the one that's never used. When you're unprofitable, you're almost 100% sure to not be attacked even by the strongest players in your universe.
Exceptions are:
*above mentioned "turtle-hunters". They will smash you to pieces just for fun.
*You play in a special universe where a certain % of the defense cost goes to a Debris Field when it’s destroyed (defense-to-Debris Field universes). In such universes a big defense is like a free BBQ for all players with a strong fleet, as defense can't run away from an attack.


==Chance of reconstruction==


As said, defensive units can't fly, so they can't be saved from attacks. But if they are destroyed during an attack it’s not the end. In OGame every type of defense has a chance of 70% to be repaired after it was destroyed during an attack. If you use the premium-feature "Engineer" the chance is 85% (see <<Premium Features>>).


This feature doesn't allow your enemies to wipe out your defense in just 1 run. They have to fly numerous attacks against your planet before everything is gone. Another way to destroy defense is via using Interplanetary Missiles.


==The different defensive units==


Even though all defenses have the same purpose, to protect your planet from enemy attacks, each type of unit has own particularities. It’s basically the same as with fleets. All units play their own important part, but only in combination with the others they are the most effective.


Rocket launcher
The first available defense unit in OGame is the Rocket Launcher. It's the cheapest unit too. It is, especially in the later game-stages used as Cannon Fodder... huge masses to spread enemy fire and give the big guns a better chance to survive and hand out damage.
Its biggest disadvantage is, that some ship-types (especially Cruisers) have a very high rapid-fire against them. So you should combine them with Light Lasers.


Light Laser
The Light Laser is the second Cannon Fodder-unit. Marginally more expensive then the Rocket Launcher, it has a bit better stats and Cruisers don't have rapid-fire against them, but destroyers do.


Heavy Laser
Too expensive for the role of Cannon Fodder, it still shouldn't be missing in any good defense. Especially good against Light Fighters as each shot of a Heavy Laser can kill 1 Light Fighter (mind that the same value in docked Cruisers will be even more effective against the Light Fighter swarms).


Ion Cannon
No defensive unit has stronger shields then the Ion Cannon, making it very durable. Its high Crystal costs in addition with its low attack-strength make it less popular than Heavy Lasers or Gauss Cannons. Mind Crystal is the scarcest resource in game.


Gauss Cannon
Long before you have access to the Plasma Turret you'll be able to build Gauss Cannons, the second-strongest defensive-units. Their good attack power makes them especially good against Cruisers and if you build quite big numbers, against Battleships. They are also effective to fight the Deathstar.


Plasma Turret
The biggest gun with the highest price. The needed researches alone are a fortune for players in the early days of their career, and the Turret itself is pretty expensive too. But what you get in return is the strongest gun, powerful enough to fend off even big ships like Destroyers or Deathstars. Most efficient when you add Cannon Fodder to protect it as long as possible to allow it to deal out huge amounts of damage. It's the only gun that doesn't trigger Deathstar's rapid fire.


Small Shield Dome
Shield domes do absolutely no harm to enemy ships (except probes), but that isn't their purpose anyways.
In the earlier game stages even 1 Small Shield Dome alone can fend off a whole enemy fleet, in case it consists only of Cargoes. That is because those ships lack the attack strength to penetrate the shield itself and thus can't destroy the Dome.
You can only build 1 Small Shield Dome per planet.


Large Shield Dome
What goes for the Small Dome goes for the Large Dome too… but just in a bigger scale. Even Light Fighters in any amount can't do any harm against the Large Dome and have to fly home empty-handed.
You can also build only 1 Large Shield Dome per planet.


Anti-Ballistic Missile
Anti-Ballistic Missiles are a special type of defensive units. They're not designed to fight enemy ships, but instead to shoot down incoming Interplanetary Missiles. Each Anti-Ballistic can take out 1 Interplanetary Missile (see <<Interplanetary Missiles>> for more).


Interplanetary Missile
With Interplanetary Missiles you can clean an enemy’s planet from defense without launching a single ship. They destroy the defense without rebuilding, so when using them you can wipe out the defense completely (see <<Interplanetary Missiles>> for more).