Defense Tips

General

In OGame-style games, defense plays an important role in protecting the resources on your planets. The main job of defense is to shoot down enemy ships. This sounds very simple, since a single defense unit is generally better than a single ship unit — i.e. 1 Rocket Launcher is better than 1 Light Fighter. But what do you do when you're attacked with 200 Battleships?

For Players Below 3,000 Points

For newbies, defense doesn't yet play a central role, since they can't be attacked by overly strong players. But they can be attacked by roughly equally strong raiders, who usually have a larger fleet. With the right number of guns in the right ratio, however, you can defend well against raiders, or at least make yourself unattractive as a target.

Rocket Launcher: 75
Light Laser Cannon: 75
Heavy Laser Cannon: 20
Ion Cannon: 20 (as long as enough crystal is available; otherwise increase the number of Heavy Laser Cannons instead.)
Small Shield Dome: 1

With this defense, you can fend off the following fleet:

At double the number of ships, you still get a draw and lose almost no Heavy Lasers. The claim that Ion Cannons hold off cruisers better than the Heavy Laser due to their improved shield is wrong. Ion Cannons currently cost too much crystal. If we convert the crystal at the usual 2:1:1 trade rate into standard metal units (SMU), we notice that an Ion Cannon costs 14,000 SMU, while a Heavy Laser only costs 10,000 SMU. Through their increased firepower, though, they do offset the disadvantage of their weaker shield.

The examples are based on equal research levels.

For Players Up to 5,000 Points

Once you have more than 3,000 points, you should already research the Gauss Cannon and, if possible, the Large Shield Dome as well, since they're advantageous in upcoming battles. You should also expect that the first raider will have their first Battleship by this point. But with the following setup, you can handle Battleships well.

With this, you can fend off:

You would win this battle a large percentage of the time, but there's also a chance of a draw, since in the last round 1 Battleship can't be shot down. However, the opponent's losses are many times higher than your own.

For Players Up to 10,000 Points

At this stage, you shouldn't expand your defense too much, since you can now be attacked by all players. It's better to research the Hyperspace Drive and Plasma Technology to be able to build better ships and defense installations later. You should only build a few Gauss Cannons and some cannon fodder.

Defense:

Rocket Launcher: 250
Light Laser Cannon: 200
Heavy Laser Cannon: 40
Gauss Cannon: 7
Ion Cannon: 40
Small Shield Dome: 1
Large Shield Dome: 1

With this, you can fend off:

Small Cargo Ship: 50
Large Cargo Ship: 30
Light Fighter: 150
Heavy Fighter: 100
Cruiser: 50
Battleship: 20

This battle would end in a draw with high losses for the attacker, while the defender only loses 3 Gauss Cannons; the shield domes remain intact. However, the cannon fodder gets wiped out.

For Players Up to 50,000 Points

At this stage of the game, the player normally reaches Plasma Technology. They also have a high level of Hyperspace Drive, allowing them to build several ship classes. Even so, defense still plays an important role.

Defense:

With this, you can fend off:

You win the battle 41% of the time, otherwise it's a draw; the attacker loses every ship except 1 Destroyer. The defender loses 7 Gauss Cannons, but no shield domes or plasma turrets; the cannon fodder is largely wiped out.

Or: 250 Destroyers -> draw, the attacker loses 1/3 of their Destroyers, but the defender loses 10 Plasma Turrets and 50 Gauss Cannons!

Or: 250 Battleships -> the defender wins!

Or: 200 Battlecruisers -> the defender wins!

Or: 1 Death Star -> draw, the defender loses 1/4 of the cannon fodder, 13 Gauss Cannons and 4 Plasma Turrets!

Or:

Battleship: 100
Battlecruiser: 50
Destroyer: 20
Death Star: 1

Draw -> the attacker loses every ship except the Death Star. The defender loses 4 Plasma Turrets and 13 Gauss Cannons, but again no shield domes.

Players With More Than 50,000 Points

For players with more than 50,000 points, it's advisable to focus solely on the fleet, since even the best defense can be wiped out with Bombers or Death Stars (RIPs). I wouldn't recommend abandoning defense entirely though, since especially for players with little time who can't save their fleet, it's a huge time saver. For example, with a defense of 60k Rocket Launchers, 40k Light Lasers and 1k Gauss Cannons, plus 320 Plasma Turrets (a defense fitting a 5-million-point player), you can, at equal research levels, wipe out a fleet of 1.5k Destroyers and 50k Light Fighters 100% of the time without major losses to the big guns, i.e. Plasma Turrets and Gauss Cannons. In this battle, the attacker's losses are 9.2 times as large as the defender's!

Cannon Fodder

Cannon fodder is an enormously important unit in defense. At the start of the game, only Rocket Launchers and Light Laser Cannons count as cannon fodder, but later on Heavy Laser Cannons and Ion Cannons join them, since they can no longer deal enough damage against the stronger ships (Battleships and so on).

In a good defense, cannon fodder and the big guns like Gauss Cannon and Plasma Turret should complement each other in a good ratio. The job of cannon fodder is to draw the damage onto itself each round, so the expensive guns aren't damaged. So it's no surprise if 50 or more units of cannon fodder are lost per round while the Plasma Turrets survive.

The ratio of cannon fodder to the bigger guns should be 5-8:1!

Anyone who builds too little cannon fodder will also lose their bigger guns in battle!

What Makes Good Cannon Fodder?

Rocket Launcher: These are well suited as cannon fodder, since they cost very little but also aren't too bad. Stronger players usually have excessive metal reserves, which they then invest in Rocket Launchers. For cost reasons, you can build 75-80 Rocket Launchers per 100 Light Laser Cannons, since the laser cannons are still cheaper. Rocket Launchers are equally good (or equally bad) against all ships, only falling short against Cruisers and Bombers. Don't be surprised if Rocket Launchers die in large numbers per round, though, since they have the weakest hulls and shields. But they're so cheap that they can keep up with Destroyers in terms of price-to-performance:

20 Rocket Launchers easily handle a Destroyer, losing 4 Rocket Launchers in the process...

Light Laser Cannon: The Light Laser Cannon is the best choice for cannon fodder, since it has the best price-to-performance ratio of all guns. It's somewhat better than the Rocket Launcher but more expensive, since crystal is usually scarce. However, it's not much better, since it also stands no chance against the bigger ships. You can/should build these guns in bulk, meaning you should have more Light Laser Cannons than Rocket Launchers.

45 Light Laser Cannons will guaranteed handle a Destroyer, losing 21 in the process... (though the Destroyer has a rapid fire of 10 against Light Laser Cannons, so it's no surprise that so many die).

Heavy Laser Cannon: The Heavy Laser Cannon counts among the mid-tier guns and is no longer quite as cheap. It's stronger than the Light Laser Cannon, but you shouldn't build too many, since at 2.5x the firepower compared to the Light Laser Cannon, it costs 4x as much! So it's usually better to invest in Light Laser Cannons instead. Heavy Laser Cannons do complement any defense though. It's best to build 1 Heavy Laser Cannon per 3 Light Laser Cannons.

8 Heavy Laser Cannons will handle a Destroyer, losing 4 in the process.

Ion Cannon Ion Cannons aren't practical as cannon fodder due to their high crystal share. It's better to trade the crystal away with other players. Why is explained further above.

Big Guns

Only the Gauss Cannons and Plasma Turrets count as big guns. They're expensive, but hit hard and have good shields. They're the terror of every raider. Here are a few tips on how to use them most effectively.

1). Pay attention to the right ratio: 1 Plasma Turret per 3 Gauss Cannons.
2). 1:5-8 to cannon fodder
3). Plasma Turrets in particular are terribly expensive, but they're worth it!
4). Anyone with enough Plasma Turrets can handle any Destroyer fleet.
5). It only takes 36 Plasma Turrets or 218 Gauss Cannons to handle a Death Star (RIP) (at equal tech levels).
6). A Death Star (RIP) can only destroy 1 Plasma Turret per round, but it has rapid fire against Gauss Cannons!

Missile Silos

At the latest once you start building Plasma Turrets, you should also think about Missile Silos and make sure you always have enough Interceptor Missiles, otherwise the raider will simply use Interplanetary Missiles to make sure their fleet no longer runs into big guns. This can be especially frustrating for the first Plasma Turrets you painstakingly saved up for.

Shield Domes

Shield domes are very useful in new universes for fending off enemy attacks, but in older, more advanced universes they're practically useless.

Small Shield Dome

Large Shield Dome

Risks

Especially in universes where destroyed defense also goes into the debris field, defense can also carry risks, since 30% of destroyed defense installations end up in the debris field there. A raider will of course factor this into their cost-benefit calculation, especially if you've built a lot of defense with a high crystal share on your planet. This is why, in such universes, the Rocket Launcher gains extra appeal as cannon fodder, since metal is the most readily available resource and therefore the least sought-after when raiding.

Adapted and cleaned up from owiki.de (GNU Free Documentation License 1.3), a general OGame community wiki — the conceptual explanation applies generally, but specific numbers/formulas may differ from the pr0game source code and are not verified.