Defense

Use of Defense Installations

Defense installations (also: defense or def) are units built permanently on a planet or moon that defend it against attacking fleets. They're built in the Shipyard and cannot be canceled once construction has started.

Defense in battles includes your own ships, allied fleets holding in orbit, as well as any built defense installations (guns and shield domes). Defense fires automatically.

Interceptor Missiles (also A-Missiles) also count as defense, but serve exclusively to destroy enemy Interplanetary Missiles, which in turn can only be used against defense installations.

Unlike buildings, defense installations don't take up any fields on the planet. Unlike fleets, they cannot be moved and therefore also cannot be saved.

Overview of Defense Installations

Base Values

Unit	Cost			Values			Rapid Fire from (*)
Unit	Metal	Crystal	Deuterium	Structure	Shield strength	Attack	Cruiser	Destroyer	Bomber	Death Star
Rocket Launcher	2,000	0	0	2,000	20	80	10	1	20	200
Light Laser Cannon	1,500	500	0	2,000	25	100	1	10	20	200
Heavy Laser Cannon	6,000	2,000	0	8,000	100	250	1	1	10	100
Ion Cannon	5,000	3,000	0	8,000	500	150	1	1	10	100
Gauss Cannon	20,000	15,000	2,000	35,000	200	1,100	1	1	5	50
Plasma Turret	50,000	50,000	30,000	100,000	300	3,000	1	1	5	1
Small Shield Dome	10,000	10,000	0	20,000	2,000	1	1	1	1	1
Large Shield Dome	50,000	50,000	0	100,000	10,000	1	1	1	1	1

Interceptor Missile	8,000	0	2,000	8,000	1	1	-	-	-	-
Interplanetary Missile	12,500	2,500	10,000	15,000	1	12,000	-	-	-	-

(*) All ships not listed have a rapid fire of 1 against all defense installations.

Requirements

Listed here alongside the primary requirements are also the secondary requirements. The latter are highlighted in color.

Unit	Buildings			Research and lab level
Unit	Robotics	Shipyard	Missile Silo	Energy Tech	Laser Tech	Shield Tech	Weapon Tech	Plasma Tech	Ion Tech	Lab
Rocket Launcher	2	1	-	-	-	-	-	-	-	-
Light Laser Cannon	2	2	-	2	3	-	-	-	-	1
Heavy Laser Cannon	2	4	-	3	6	-	-	-	-	1
Ion Cannon	2	4	-	4	5	-	-	-	4	4
Gauss Cannon	2	6	-	6	-	1	3	-	-	6
Plasma Turret	2	8	-	8	10	-	-	7	5	4
Small Shield Dome	2	1	-	-	-	2	-	-	-	6
Large Shield Dome	2	6	-	-	-	6	-	-	-	6

Interceptor Missile	2	1	2	-	-	-	-	-	-	-
Interplanetary Missile	2	1	4	-	-	-	-	-	-	-

Calculated Values

Since defense installations naturally lose most battles (otherwise, after all, they wouldn't be attacked in the first place), it's especially important for defense installations to deal as much damage as possible in as few combat rounds as possible. The attacker should ultimately be able to gain as little as possible. Defense is therefore deterrence!
The following overview shows the survival probability of a ship when hit by the corresponding defense installation. The calculation was done at equal technology levels.

Survival Probability of Ships When Hit
Unit	Spy	SCS	LF	HF	LCS	Cru	BS	BC	Bomber	Des
Rocket Launcher	20%	100%	100%	100%	100%	100%	100%	100%	100%	100%
Light Laser Cannon	0%	100%	100%	100%	100%	100%	100%	100%	100%	100%
Ion Cannon	0%	65%	65%	100%	100%	100%	100%	100%	100%	100%
Heavy Laser Cannon	0%	40%	40%	100%	100%	100%	100%	100%	100%	100%
Gauss Cannon	0%	0%	0%	0%	10%	61%	100%	100%	100%	100%
Plasma Turret	0%	0%	0%	0%	0%	0%	53%	63%	67%	100%

For every 1,000,000 invested standard metal units (SMU, at a 2:1:1 exchange rate), defense installations therefore destroy the following number of ships per round at maximum fire distribution. (The respective best defense installations are highlighted in bold.)

Ships Destroyed per 1M SMU of Defense (2:1:1 Rate), One Hit Each
Unit	Spy	SCS	LF	HF	LCS	Cru	BS	BC	Bomber	Des
Rocket Launcher	400	0	0	0	0	0	0	0	0	0
Light Laser Cannon	400	0	0	0	0	0	0	0	0	0
Ion Cannon	71.4	25	25	0	0	0	0	0	0	0
Heavy Laser Cannon	100	60	60	0	0	0	0	0	0	0
Gauss Cannon	18.5	18.5	18.5	18.5	16.7	7.2	0	0	0	0
Plasma Turret	4.8	4.8	4.8	4.8	4.8	4.8	2.2	1.8	1.6	0

Repairing Defense Installations

[...] After a battle, there is a chance of up to 70% that disabled defense installations can be repaired again.

A defense installation deactivates itself once its hull has been damaged too severely. This works analogously to the destruction of ships.

Unlike with ships, however, the chance after a battle is 60-80% that disabled defense installations can be repaired. If there are more than 10 units of a given type of defense installation, the 60-80% repair rate is applied to that group as a whole. For up to 10 defense installations of one type, the probability is calculated individually for each. This can mean that, in the best case, all 10 Rocket Launchers get repaired after an attack, or in the worst case, all 10 Rocket Launchers are permanently destroyed.

An engineer officer halves these losses to defense installations.

In universes where a share of destroyed defense installations' resources goes into the debris field, less defense is typically built, because a "def kill" pays off more (pr0game's current universes each define this share individually — see the per-universe settings on the universe overview page).

Game Strategies

Opinions in the community regarding defense are very mixed. Some build no defense at all, others build it up massively ("deffing"). Depending on playstyle, the following strategies emerge:

Fleet saving: You send all your resources on a long journey every day. Otherwise, you build just enough defense for the mines' overnight production.

Downside: resources aren't available while in transit.

Deffing: You build so much defense that the raider needs a much larger fleet and therefore also more deuterium, which throws off their cost-benefit calculation. Simulations are also less accurate with large defenses, which is an additional risk for the raider.

Downside: Defense doesn't work for you! Also, "deffers" aren't very popular. Deffing is occasionally cited as a reason for war. Additionally, the combat coalition system allows players to team up into huge Death Star or Bomber/Destroyer "def-clearing" fleets.

Middle ground: You build just enough defense that you only need to transport away resources about once a day without risking being raided (deterring newbies and casual raiders). The resources then usually end up being collected in a central "bunker" anyway.

Rapid-fire ships used as defense: In addition to normal defense, you park Destroyers, Battlecruisers and, to a lesser degree, Cruisers for extra firepower. The downside of normal defense is that defense installations have no rapid fire. So a few hundred Battlecruisers can easily destroy a thousand Battleships or Cruisers. Cannon fodder made of Light Fighters should of course be avoided entirely, relying instead completely on defense installations like Rocket Launchers or Light Laser Cannons.

Downside: destroyed ships go into the debris field. These ships could therefore even attract attackers rather than deterring them.

Rocket Launchers and Death Stars: The weakness of most defenses lies in their vulnerability to Death Star fleets, against which they often can't inflict any losses at all. The only effective protection against this is Death Stars stationed behind your defense. Thanks to their immense rapid fire, they can also deal heavy damage to all other fleets, as long as they survive. That's why they need to be protected by a correspondingly large amount of cannon fodder.

Build Strategies

A very good ratio of defense installations for fending off Destroyer fleets has been calculated in various community discussions.

One calculated ratio:
100 Rocket Launchers
  5 Heavy Laser Cannons
  1 Gauss Cannon
  1 Plasma Turret

Another community calculation aimed at securing overnight production yielded a different defense ratio.

That calculated ratio:
 75 Rocket Launchers
150 Light Laser Cannons
  8 Gauss Cannons
  1 Plasma Turret

Which build strategy to follow is largely a matter of taste. Some players build practically no defense — especially, of course, in universes where destroyed defense goes into the debris field, which are becoming increasingly common — others rely on strong defense, up to and including a full "bunker". The second ratio shown above is fairly expensive and offers no effective deterrence against Light Fighters, Heavy Fighters, Bombers, Battleships, Battlecruisers and Destroyers. On the other hand, this variant is not a bad intermediate solution for a balanced defense, especially relatively early in a universe's life.

Under the competing approach, extensive simulation produced one of the best solutions for a defense strategy under current rapid-fire rules. Light Lasers only have an advantage over Rocket Launchers when fighting Cruisers; Gauss Cannons essentially never have an advantage over Plasma Turrets.

In general: cannon fodder exists only to prolong a battle — that is, to maximize the damage output of the big guns. The cannon fodder's own damage output plays almost no role, meaning the shield values and attack strength of Rocket Launchers and Light Lasers are nearly irrelevant. Because of how battles are simulated, concentrated fire is always better than spread-out fire.