Systems can be upgraded and need power bars (given by your reactor) to function. They can be damaged and destroyed, which means the system will not be fully functional (or not at all) and will need to be repaired. Some systems will always be present on any ship, others won't, and will have to be purchased at a store. Your ship can only have 8 systems (subsystems do not count towards that score).

If a system or subsystem is completely destroyed by fire or boarders, your ship will take one extra hull damage. There is no extra hull damage if it's destroyed by laser or beam weapons.

Usually, systems should only be upgraded if you're going to use the extra power invested in this system. For instance, getting two shield power to have one extra shield layer should only be done if you can also buy (or redistribute from your reactor) the two power bars necessary to power the system.

Basically: you shouldn't buy a system upgrade if you can't or won't power it.

There is, however, a very exception to this rule, which is the concept of value points (or buffer points).

A value point is an upgrade to a system that is not meant to be immediately (or ever) used, but to prevent the system from functionning sub-optimally if it takes damage. Let's say you have Cloaking and are only using it at level 1 to cloak enemy missiles and recharge it quicker. If you take any system damage in Cloaking, it will immediately be broken and you will not be able to use it until you have repaired it. Whereas having a level 2 cloaking means that taking one point of damage in Cloaking will not immediately break it, and you can still use it for the rest of the fight.

Weapons hugely benefit from value points, as you'll often be relying on several weapons to beat enemy ships. If one of your weapons goes offline, the strength of your volley can severely be diminished or even nullified, and you have to wait both for the system to be repaired and for the weapon to charge again... which is not good, as most of the time, you want to end fights as quickly as you can.

In very niche situations, you can also want to invest in a value point for shields, but most of the time you'll just want to hold on to your scrap to be able to buy the whole shield layer when you can afford it (or something else interesting from a store).

This is especially useful because there are very few weapons that can deal two points of damage to a given room. The Small Bomb, the Heavy Laser, the Halberd Beam (provided to have no shields active when it fires) and the Glaive Beam (provided you have at most one shield bar active when it fires) are the only weapons able to do that.

Value points are inherently inneficient against ion damage, as it disables the system for a given period.

Buying value points isn't a no-brainer choice. It should be considered wisely, as it is :

• expensive (most of the time) : a value point in a level 6 weapons system costs 90 scrap, which could be used to upgrade and power level 3 Hacking, which is always better ;
  
• buying something you're not actively using, being instead something that passively protects you - sometimes - from bad situations.

For instance, the weapons value points in early sector 1 on the Stealth B isn't a trivial purchase, as you also want to save for level 3 Cloaking, Shields, Hacking, and other weapons.

That being said, when you reach the flagship you usually want to have value points in most systems (especially Cloaking, Mind Control, Oxygen and even your medical unit).

• Can be manned
  
• Max power: 8
  
• Cost: 125 scrap
  
• Not present on every ship

You know them: the nice little blue bubbles that keep your ship safe… For a time.
It will protect you against ions, lasers, against beams if your shields are as powerful (or more) as the beams, but not against bombs and missiles.

Every ship starts with one shield bar (two shield bars for the Mantis B) apart from the Zoltan B and the Stealth Cruisers. The Zoltan B has « weak » shields, meaning you start with no shield bars and the first upgrade is more expensive than it usually is (100 scrap).

The Stealth Cruisers don't have shields system at all, which means you will have to buy it (for 125 scrap) at a store. Usually getting them at a store isn't too hard, provided you have the scrap.

This system functions with pairs of power bars. To gain a shield bar, you need to purchase two levels in the Shields system, and power them. If you take only one, you cannot power it, so it will only be a value point.

If you deactivate your shields, they will deactivate pair by pair (two power bars each time). If the system is damaged, or if you have only one power bar where you need two, you will lose a shield bar. The room with the Shields system is the very room (with Weapons) you MUST protected from intruders, fire, and all forms of damage. If you let something bad happen in this room, you will pay it quickly.

By the time you reach the Flagship, you should have at the very least three shield bars. The fourth layer is expensive (180 scrap + 2 power bars (20-35 scrap)), but critical to protect you against the power surges in phases 2 and 3.

If you're using a turtle build (alternating usage of level 3 hacking on weapons and level 2 cloaking to be invulnerable to enemy weapons), it is fine behind one shield bar "behind", even against the flagship - provided you have enough firepower to kill the ships in your sector, obviously.

Remember that the Halberd Beam can pierce one shield bar, and the Glaive Beam can pierce two. They will deal one point of damage less per shield layer pierced.

Having shields up reduces hull damage and fires caused by solar flares.

Be careful with Zoltan crewmembers, as moving them out a room will de-power it.
It should also be noted that Zoltan are ion-resistant, which means any power bar given by a Zoltan to a system can't be removed by ion damage (for instance, having two Zoltans in the shield room will grant you one shield bar that resists to ions no matter what).

Generally, you want to have two shields bar by the end of sector one / beginning of sector two, three shield bars by sector 5, and four shield bars by sector 8.

This system should be manned, but has less priority than piloting, engines and weapons. Training is a nice plus, but doesn't matter too much.

What's efficient against enemy shields?

Shields are often (but not always) your number two target, after Weapons, on the enemy ship, simply because once they are down, you can attack any system you wish, and also use Beam weapons at the height of their power. You should always have enough firepower to take down the average shields in the system you're roaming. In Hard, enemy ships start to have level 2 shields by sector 3, level 3 shields by sector 5, and level 4 shields by sector 7.

You don't necessarily need to break enemy shields, as long as you have enough shots to take them down and then damage systems. For instance, the Stealth A can basically take on level two shields, as it has the two shots from the dual lasers to take shields down and the mini beam to deal up to four damage.

Things that are really great against shields :
- Flak Mk. I (better than Mk. II because it's cheaper, more power-efficient, more accurate, and quicker to fire). A combo of good laser weaponry (Burst Laser Mk. III alone or a Burst Laser Mk. II and another laser weapon) is also nice.
- Hacking.
- Status effects (fires and breaches) to make the system harder to repair.
- Mind Control to prevent the repairs.

• Can (and should) be manned
  
• Max power: 8
  
• Cost: null
  
• Present on every ship

Every ship starts with engines, for obvious reasons. Having good engines make your FTL drive charge faster, grants your ship more evasion abilities, and it also can serve in some (rare) events.

Engines are the one system you generally want to upgrade just after upgrading your shields to get two shield bars. The first upgrades are very cheap (10, 15 scrap for level 2 and 3) and it grants you a evasion. A faster charging FTL is also nice when you have to flee from ♥♥♥♥♥♥♥♥ fights.

Note that is the Piloting is destroyed or is level 1 and not manned, your evasion percentage will be zero. If piloting is destroyed or not manned (regardless of its level), your FTL won't charge.

The ideal is to have a minimal evasion percentage of 40, as it grants you guaranteed dodges whenever you use Cloaking and its 60 percent evasion bonus. Manning this system is very important and training is very valuable.

What's efficient against enemy engines?

If you want to target your enemy's engines, it's to prevent him either from:
- escaping with FTL.
- dodging your shots.
Either way, don't target the enemy's engines, but the pilot's chair. Why? Because you have to completely destroy the system to prevent the enemy from dodging or escaping, and the pilot's chair will be level 3 maximum (and often level 1 or two), so it will take just a few shots to destroy it completely. And that will always gain you time, which can be crucial to the issue of the fight.

The same applies to using Hacking and Mind Control to drop the enemy evasion.

• Can (and should) be manned
  
• Max power: 8
  
• Cost: null
  
• Present on every ship

That's another system you want to keep safe from any trouble, especially boarders. Weapons (especially hull damaging ones) are the only thing that can always give you a chance to kill a ship.

This system is on every ship, at level one from four. Sometimes it's a weak system and you need extra scrap (40) for the first upgrade.

This system should be upgraded cautiously. Unless you want a value point, you must always upgrade it AFTER getting the weapons that need extra system power and AFTER making sure that you have enough reactor bars to power them.

If you have a Zoltan crewmember in the weapons room, his power bar will always be used to power the first weapon slot. Note that you can decide which weapon is in which slot, and thus, which weapon is powered by the Zoltan. However, having a Zoltan in the weapons should be avoided, as moving them out of the room will de-power a weapon.

When the weapons take damage, weapons are de-powered from right to left, so put the weapon you absolutely want to use to the left.

As ScottOnesieWilson stated in his very good weapons guide[docs.google.com], It is important to have a balanced weapon system, with "1-2 Shield Removal weapons, and 1-2 weapons fulfilling a secondary role [system disruption, hull destruction or crew elimination]". I encourage you to have a close look at his guide to learn more about which weapons to use!

This system should always be manned, and training is very valuable.

What's efficient against enemy weapons ?

Weapons are your first target on the enemy ship most of the time, simply to prevent them from hurting you. Your shields / defense drone(s) / Zoltan shields will not always be enough to block everything the enemy has to send your way.

Remember that the flagship hasn't got a single weapon system. Instead, it uses 4 different artillery systems, which simply means you cannot strike all his weapons at the same time. Missiles (and then, if you can, Ions in phase 1) are the first you want to target, with the other two being less dangerous.

- Hacking. It will show you the enemy's weapons charge regardless of your sensors' level, so you can trigger the hacking and discharge the weapons just before the shot(s) you wish to avoid.
However, if the enemy's defense (shields or evasion) proves too difficult for you to bypass, you will have a hard time killing the ship.
- Status effects like breaches and fires.
- Mind Control to block repairs.
- Obviously any damage your weapons can give goes in there first.

• Cannot be manned
  
• Max power: 3
  
• Cost: 50 scrap
  
• Not present on every ship

These are two variants of the same objective : keeping your crew alive.
- The Medbay, when powered, heals the crew inside it. The more the Medbay is upgraded, the quicker your crew heals.
- The Clone bay, when powered, will clone every dead crewmember on your side, after some time and with a skill penalty (on every skill). It will also restore some health points to your injured crewmembers when FTL jumping, whether the clone bay is powered or not.
If the Clone bay is destroyed or unpowered and one of your crewmembers dies, you will have just a few seconds to repair it and repower it. If you don't do it in time, your crewmember will be definitely gone, unless you have the Backup DNA Bank augment.

Obviously, you don't want that to happen, so you should always mind whether the enemy can destroy your clone bay or not (Small Bombs, in that regard, are very dangerous).

Every ship but the Slug B has a Medbay. The ships added in the advanced edition (all C-Layouts, and Lanius ships) will have a Clone bay.

The Medbay will not heal enemies or your mind-controlled crewmembers, so fighting in your Medbay is one of the best ways to counter an enemy boarding (with venting rooms). Speaking of which, you can force boarding enemies into your Medbay by venting other rooms on their path, since they will flee rooms without oxygen. Unless they are Lanius, of course.

If you have a Medbay and want a Clone Bay (or vice-versa), you can purchase one at a store (provided it sells it) for 50 scrap. The Clone Bay will replace your Medbay, and any upgrades done to the Medbay will carry over to your Clone Bay (and vice-versa). However, you usually don't want to swap your medical unit for another one, as it's expensive and it's better do just use what you already have.

Something very important with the Clone bay is the events. As you already know, there are a ton of events in the game in which you can lose a crewmember (for instance, the dreaded Giant Alien spiders).
In most (but not all, so be careful and check the wiki whenever necessary) of these events, your crewmember will be revived by the Clone bay even if it's not powered when you get the event.

The Clone bay will not clone a crewmember located on an enemy ship that jumped away.

Enemy clone bays will clone boarders generated by an event.

Usually uprading your medical unit isn't very useful (even the value point for the flagship is less important than a value point in Cloaking, Oxygen, or Mind Control), even with boarding ships. An argument can be made to upgrade the Clone Bay to level 2 with a boarding ship if you're ahead on scrap.

What's useful against enemy med/clone bays ?

- Obviously weaponry.
- Hacking and then boarding the room.
- Gather all the enemy crew in the Shields Room using Mind Control (see Mind Control below) then move your boarders into the medical unit to destroy it.

If you're just going to kill ships, you don't care about them having a medical unit.
If you're trying to get crewkills with your weapons, the presence of a medical unit can make it a bit tedious if you both have to deal with that and an annoying missile weapon.
If you're trying to board the enemy ships and kill their crew that way you have to have an answer to the medical unit, otherwise you can only flee or kill the ship.

Hacking the Medbay will cause it to poison the enemies inside it, which can be pretty useful, but you may also just do that to abuse the door locking, which can be very valuable when boarding.

• Cannot be manned
  
• Max power: 3
  
• Cost: null
  
• Present on every ship

It's so obvious that we could forget it. There's no air in space, and your crewmembers, apart from the Lanius, all need oxygen to breathe and live. So there's a life support / oxygen system which fills and refills your ship with oxygen.

You want to keep a close eye on this one, as a dead Oxygen system can quickly snowball in a bad way for you. That beind said, it's actually not that bad to lose the O2 - it depends on the situation, but usually losing shields or weapons is worse. In fact, you can even de-power your O2 to use the power bar elsewhere (to power a weapon, a system, or the engines for extra evasion) at the beginning of a fight, quickly kill the enemy ship and then refill the O2. It's completely valid as long as you kill the enemy ship quickly - if not, simply swap power again.

If your crew is only Zoltans (low health) or Mantis (slow repairs), you should repair a broken O2 very quickly, whereas having two Engis gives you a lot more breathing space (no pun intended).

It's important to note that if your Oxygen system is hacked by a level 3 hacking, a level 1 Oxygen system will not replenish the air fast enough and your crew will suffocate and die unless you end the fight quickly. For this reason, your Oxygen should always be level 2 (or more, but the third upgrade isn't necessary) when you reach the Flagship.

What's efficient against enemy life support ?

- Lanius Boarders
- Weaponry
- Hacking

Usually you target the enemy O2 to get crew kills. A good way to do this is to hack the Oxygen, fire your weapons and start hacking just before the Oxygen is destroyed. You can't hack a destroyed system, but an in-progress hack will keep going even if the system is destroyed, so that trick can save you precious seconds when trying to get a crew kill.

Even Ion Damage, if important enough, can disable the O2 for a crew kill.

• Cannot be manned
  
• Max power: 3
  
• Cost: 150 scrap
  
• Not present on every ship

An excellent system, though expensive. Cloaking gives you automatically 60 % evasion (regardless of the status of the pilot's chair!) for all its duration (5, 10 or 15 seconds depending on the level).

It means that if you have good engines and/or skilled crew in the engines and/or piloting rooms, you can get to 100 % evasion, or close to it, for a few seconds. Obviously, being able to dodge a given attack is very valuable, especially against missiles since your shields won't stop them.

The cooldown starts when the cloaking deactivates, not when you cloak. The longer you cloak, the longer the cooldown.
For this reason, you usually want to keep your cloak at level 1 (if possible with a value point) since you will most likely use it to dodge only one attack like a missile or the flagship's super weapon in phase 3.
However, if you want to use a turtle build (alternating usage of level 3 hacking on weapons and level 2 cloaking to be invulnerable to enemy weapons), you need a level 2 cloaking.
Level 3 cloaking is almost never necessary (Stealth B is basically the only exception).

Level 2 cloaking is also very useful to fully dodge the drone power surge of the flagship in phase 2.

When you cloak, enemy weapons stop charging, anti-ship enemy drones will drift, and boarding/hacking drones will simply stop until you reappear. Cloaking just after en enemy's volley can give you a two volley advantage as their weapons stop charging while you're cloaked.

That means if you want to dodge one or several shots, you must activate cloaking after those shots are fired.

If you instead want to prevent the enemy weapons from charging (to counter a beam weapon, or to give your own weapons time to charge like on the Stealth B), you can cloak early.

If your shields are down and the enemy is about to shoot at your ship with a beam weapon, you should cloak to regenerate your shields.

Cloaking also prevents the enemies from boarding your ship or mind controlling your crew. This does not stop an already active mind control.

Firing your weapons during cloaking reduces the time left before you reappear, so you also want to be aware of that if an ASB is about to fire.

Cloaking also blocks the Flagship's artilleries from charging but NOT his power surges in phases 2 and 3, as they are triggered on an independent timer.

What's useful against enemy cloaking ?

It's often better to play around enemy cloaking than to directly target it, as you have more important targets.

Enemy ships will always trigger their cloak at the beginning of the fight, which will let you know if it's level 1, 2 or 3. With that information in mind, you can also estimate when their cloaking will reactivate and time your volleys accordingly. Keep in mind that the AI will always activate cloaking as soon as it's available.

A beam weapon that's already firing when the enemy cloaks will not stop firing, so you can use that to your advantage.

• Cannot be manned
  
• Max power: 3
  
• Cost: 90 scrap
  
• Not present on every ship

A good, yet inconsistent system.

Even is boarding gets you crew kills and thus higher scrap rewards in most fights, boarding strategies are weak to enemy drone ships, medical units and Zoltan shields. This is especially true if you have low offensive abilities (few or no weapons, like Mantis B and Crystal B), which means it's especially true in the early sectors. For this reason, the Teleporter makes for a good late game purchase, if you can justify it (good defense, for instance with a turtle build, good weapons, and/or hacking, and/or mind control, and crew), and not a good early game purchase.

If you want to board enemy ships, you need a decent boarding team :

Double Mantis > Mantis + Crystal > Mantis + Rock > Mantis + Slug or Human >> Mantis + Zoltan/Engi (the same goes for 4-men teleporters).

Double Lanius boarding is also great, but unless you're playing the Lanius B, you'll rarely see this one.

There are a few nice things to support a boarding team:
- Hacking or Lockdown effects. To lock a room with the crew in it, so they don't escape to the medbay... or to look the crew out of a room, so you can destroy it first.
- Mind Control. It’s not very difficult to understand why. It's especially good when you know the AI will always prioritize defending the shields. If you board the shield room and mind control the crew manning them, the rest of the crew will come to help, and stay there even if you move your crew to another room, which is great with the Lanius B. Sometimes this doesn't work if there are a lot of enemy crewmembers.

If you decide to board an enemy ship, you will need to keep an eye on several things:
- Your weapons. What happens if you destroy the enemy ship with some of your crewmembers on board? They die, unless you have a clone bay.
- Artillery for the same reasons.
- The enemy’s FTL. You don’t want the enemy to jump away with your crew on board, because if that happens, they’re as good as dead, even if you have a Clone Bay.
- The enemy’s medical unit. That’s pretty obvious: if you’re boarding a ship, you don’t want its crew to regain strength during the fight.

Keep in mind that Teleporter cannot bypass Zoltan Super Shields (unless you have the relevant augmentation).

What’s useful against enemy teleporter and boarders?

Venting the ship is great (see Doors below). It can help you redirect the enemies in the (powered) Medbay, where even Engis or Zoltans shouldn't have trouble dealing with them. Even if you don't have blast doors, venting areas is good to keep the enemies moving, preventing them to cause any damage (especially to key systems such as weapons and shields). Obviously it might be easier or harder to do depending on the ship's layout.

Even if you don't have a teleporter, having a boarding team (namely 2 Mantis) is great to handle intruders, human or drones.

If there are too many boarders and you don't need to hack another system, you can hack the enemy teleporter : it will bring all intruders back to their ship at once.

Enemy boarders always go home when their health goes below a certain threshold.

• Cannot be manned
  
• Max power: 8
  
• Cost: 75 to 85 scrap, depending on the starter drone you're offered
  
• Not present on every ship

A rather bad system, though not terrible. Usually you buy it if you don't find another system and are nearing the flagship.
There are a number of reasons why Drone Control is bad :
- offensive drones are bad
- it uses drone parts, which is redundant with Hacking, and Hacking is much better
- defensive drones are mostly bad, with the exception of the Defense Mk. II being decent and the Defense Mk. I being great, and both of them still have flaws.

When buying a Drone Control system, you will either receive a Combat Drone Mk. I, a Defense Drone Mk. I or a System Repair Drone.

Drone Control is best used with the Defense Drone Mk. 1 to shoot down missiles and incoming drones, which can replace Cloaking - even if cloaking is better. But basically, you should avoid buying Cloaking if you have Drone Control and vice versa.

If you can't find a Defense Drone Mk. I, the Defense Drone Mk. II isn't terrible (especially if you got it for free). It's usually less efficient than the first version since it targets all incoming projectiles and drones get confused when trying to shoot multiple things at once, but it's decent at preserving a Zoltan Shield.

Deactivating a drone then reactivating it does not consume another drone part, which can help if you need to redistribute power during a fight.

Redeploying a destroyed drone does consume another drone part.

What’s useful against enemy drones?

Your own Defense Drone to shoot down incoming enemy drones.

Against a Defense Drone II, the answer usually is "firing a lot of projectiles and hope enough hit the target", since defense drones get confused why trying to shoot multiple projectiles at once.

To land a Hacking Drone past a defense drone, you can de-power your hacking drone just after the defense drone fires : the hacking drone will stop and the shot will miss. Then you can quickly reactivate hacking to land the hacking drone.

• Cannot be manned
  
• Max power: 4
  
• Cost: null
  
• Not present on every ship

That’s a system you only see on two ships (unless your game is modded): the Federation Ship, and the Rebel Flagship.
It acts as a single weapon system, apart from two things:
- it cannot be manned;
- it fires as soon as it is charged, and you also don’t decide where exactly on the ship it shoots.

That makes it bad, because you always want to target specific systems on enemy ship : the medical unit to get a crew kill, the weapons to disable that big missile that's going to wreck your hull, etc.

What’s useful against enemy artillery?

The Flagship has four artillery rooms. So you should take them out in order of danger (first the missiles, then the ions, then the beam, then the lasers).

It's worth noting that if you have level 1 Cloaking, dealing a single point of damage to the missile room allows you to cloak every missile volley.

• Cannot be manned
  
• Max power: 3
  
• Cost: 80 scrap
  
• Not present on every ship
  
• Alternative Edition

Best system in the game, by far. It has incredible utility, versatility and makes the game much more easier - or playable, in fact, because a lot of ships really suffer if they don't have Hacking.

Launching a hacking drone uses a drone part, so you have to be careful and try not to hack every fight when you don't need to. See Drone Control above to know how to land hacking past defense droness.

Hacking “scrambles” a system passively, and causes it to malfunction for a time (depending on the Hacking’s level) when activated.

The hacked room:
- is revealed to you with with max sensors level (even if your sensors are disabled, destroyed or non-existent), so you see the power usage of the room;
- is locked to the enemy crewmembers (your crew can move in and out without problems), who have to fight the doors to get through, just like they would on your ship ;
- loses its manned status.
You can disable / enable those effects by depowering / powering the Hacking System.

There can be other passive effects with Weapons (the weapon charge level is shown), Engines or Autopilot (the evasion percentage is shown), or Oxygen (the oxygen percentage is shown).

Hacking effects :
- Shields : shields go down (a level n-1 hacking is required to fully disable level n shields)
- Weapons or Artillery : weapons discharge over time
- Oxygen : oxygen starts depleating
- Medbay : damages crew
- Clonebay : shuts it down, killing crew if there's a cloning in progress
- Drone Control and Hacking : deactivates enemy drones, with a chance of destroying them
- Piloting or engines : evasion is reduced to 0
- Cloaking : disables cloaking, decloaks your ship
- Teleporter : any boarders are brought back to their ship at once
- Mind Control : takes control of a random enemy crew member, or disables an already existing mind control effect.
- Doors : all doors are locked on the ship
- Sensors (only on your ship) : you don't see a thing
- Battery : disables bonus energy and drains two bars from the reactor

Usually you're either hacking shields to bypass them (great if you have more beams than shield piercing), piloting to land your shots, or weapons for turtle strategies. Hacking the Oxygen is great to get crewkills.

What’s useful against enemy hacking?

The best way to avoid being hacked is to destroy the module. The Anti Drone is terrible at the job, the Defense Drone does it better (as it’s sure to destroy the module, whereas the Anti Drone tends to just stun it or even miss it). The enemy ship will launch as many hacking modules as they have drone parts.

Beyond that, there is no real counter apart from having a lot of systems on your ship, so the probability of a given system being hacked is lower.

Against the Flagship, you actually want to let the hacking drone past and then activate your defense drone. Getting hacked mid-fight by the flagship can be really bad as it can lead to weird timings if it hacks your weapons.

Shields and weapon hacks are the only one you're really afraid of, even if the later is manageable in a lot of cases.

• Cannot be manned
  
• Max power: 3
  
• Cost: 75 scrap
  
• Not present on every ship
  
• Alternative Edition

That system allows you to take control of an enemy crewmember (and, with upgrades, to boost their health and damage). They’ll attack your enemies, and they’ll be considered as an ally by your other systems. Keep in mind, however, that you won’t be able to give them orders. They will still be AI-controlled.

Like teleporting, mind control cannot bypass Zoltan Super Shields (unless you have the relevant augmentation).

You also need to see the target to control it (with sensors level 2, hacking, slug telepathy, or even teleporting a bomb).

Mind control is best left at level 1 (with a value point when you reach the Flagship) as the upgrades are just overkill.

This system is great both offensively and defensively on almost any ship. Offensively, it allows you to support boarding strategies, crew kill strategies by preventing enemys from fighting fires/breaches and gathering them all in one room, or simply drop the evasion by targeting the pilot.
Defensively, it helps you deal with most boarding situations single handedly, and counters the enemy mind control.

Mind control can be used with teleporter to kidnap the enemy crew. It's funny, but not very recommanded as it's a very slow strategy to get a crew kill.

What’s useful against enemy mind control?

You can use your own mind control as a counter.

If you can’t or don't want to, you can either keep the controled crew busy with another crewmember and/or vent the ship to keep them moving, like regular boarders, until the effect wears off.

Subsystems are all fully powered for free (so you usually want to station Zoltans somewhere else if possible). Apart from that, they act as systems.

• Can (and must) be manned
  
• Max power: 3
  
• Cost: null
  
• Present on every ship

That system must be manned in order to keep a your full evasion percentage and your FTL charging. Upgrading it gives you a fraction of your evasion bonus, even when there’s no pilot in the room. Usually you just want to take the first rank for this one. It is cheap, it prevents the system from breaking immediately and having 50% of your usual evasion chance if the pilot is away is better than nothing. Level 2 piloting can also be quickly bought if you want to guarantee the blue option for . What’s useful against enemy piloting?As I said in the engines section, if you wish to prevent the enemy from escaping via FTL or dodging your shots, you should target the piloting rather than the engines, because it will be easier to destroy it.- Weapons, especially beams. Firing the beam at piloting first, if it has enough damage to destroy it, guarantees the rest of your volley will hit.- Hacking (level 1 is sufficiant and has better cooldown) just after firing your shots.- Mind controlling the enemy pilot.[ftl.fandom.com]

• Can be manned (in Advanced Edition only)
  
• Max power: 3
  
• Cost: 60 scrap
  
• Not present on every ship (the Rock B is the sole exception)

That’s the closest thing to a security system you have in FTL. It allows you to open / close any doors on the ship at will, including airlocks.

While this looks simple in theory, it has a lot of practical uses. You can vent rooms in order to quickly put down a fire, or control where enemy crewmembers boarders are going while damaging them. You can make them suffocate until they have taken enough damage and go home, or even kill them quickly if you're looking for the crew kill.

Upgrading the system usually isn't necessary as you can use a crewmember for the same result (level 2 doors is basically enough to control boarders with venting). You can have a crewmember in doors to be ready for boarders and quickly swap them at the beginning of the fight if you see there's no need for that.

You also don't want to buy the system (on the Rock B) as it's way too expensive.

If there's a breach on your ship, opening all doors (but the airlocks) will cause the oxygen level to equalize for a time (or even completely if your Oxygen level is high enough and there are not too many breaches - do not do that with a level 1 Oxygen and two breaches on your ship), which helps for repairs.

What’s useful against enemy doors?

Usually enemy ships do not have door subsystems, and if they do, you have more important targets anyway. Remember to take this into account if you send away a boarding party, even if usually you just board one room.

• Can be manned (in advanced edition only)
  
• Max power: 3
  
• Cost: 40 scrap
  
• Not present on every ship
  
• Enemies never have it

They're pretty nice when you have them... but you can play without them. There are only two real good reasons to buy Sensors when your ship do not start with them :
- give the enemy ships (especially the Flagship) one more system to hack, because you'd rather have them hacking your sensors than your shields or weapons ;
- remove the system from the pool, so you have a higher chance of seeing other systems (namely Hacking) at a store.

Having sensors is mostly great to help with crew kills by seeing the enemy ship's interior, so you can just man the sensors mid fight if you need, and never upgrade them. With a bit of knowledge on how the AI works you can even get crew kills without sensors. For instance, a room that's only damaged will be repaired by only one crew, but more crew will come to repair a room with a status effect like fires or breaches, and you can notice that by looking at how many doors are opening on the enemy ship after you damage a system (breaches also have a sound effect, for that matter).

Usually one upgrade / manning it is enough. You don’t really need to see the enemy’s weapon charge as all weapons have visual indicators for that anyway. Same for the enemy ship’s power usage (can’t possibly think of any utility for that).

• Cannot be manned
  
• Max power: 2
  
• Cost: 35 scrap
  
• Not present on every ship
  
• Advanced Edition
  
• Enemies never have it

Great subsystem, best coupled with engines. It’s basically +2 on your reactor for 30 seconds, +4 if you upgrade it, for cheaper than two actual power bars. If you end fights quickly (which you should), you don't care too much that the power is temporary. It's also a huge advantage in a plasma storm, as it's not affected by it.

The battery is immediately reset and recharged when you jump.

Battery power is removed from systems first, and allocated last. Keep that in mind when redistributing your power : you don't want to have a shield layer powered by the battery as it's likely to let you down midfight. Usually the best usage for the battery is to keep it at level one and put the extra power into your engines.

There is not much to say about the Reactor – you simply always should have as many power bars as your ship's systems need to function, minus two if you have the Battery, minus one if you're swapping a power bar from Oxygen to Engines during fights.

Usually, upgrading a system goes with upgrading the reactor by the same amount.

Keep in mind – always buy reactor bars AFTER what you buy them for. You should always have as many power bars as your ship needs to function, but you should never have too much - otherwise you wasted scrap.

A comment to add? A mistake you think I've made? A suggestion?

Please let me know in the comments section below!