Hello, my name is Max, and I like to fortify positions. Recently, I wondered whether there was a good guide on the topic. A brief search query revealed that most discourse about defenses in Factorio is focused on the late game. Whilst it is always very interesting how other people who have finished science defend their megafactories, it struck me that it would be a good thing if there was some literature about defenses in the early and mid game. This is what I have set out to do. To illustrate my points, I will provide screenshots taken from a co-op game which has just transitioned from the mid game to the late game. Why is perimeter defense necessary? I will let this picture speak for itself.

In order to make the guide clear I must define some of my terminology.

Early game:
- Steam-powered.
- Incomplete infrastructure.
- Production occasionally still has to be done by hand.

Mid game:
- Steam-powered, possibly supplemented by solar power and capacitors.
- Infrastructure completed to player's satisfaction.
- Production automated to the player's satisfaction.

Late game:
- Nuclear-powered.
- Building is done with blueprints and construction drones.
- Logistics drones bring the player what they want directly from assemblers.

Feed Belt:
- A standard yellow belt that carries coal and ammo to the defense perimeter.

Maximum Dispersion Perimeter:
- A defensive perimeter suitable for the early game.
- Turrets dispersed as much as possible whilst remaining in eachother's range.
- Focus on enveloping the player's chosen territory as quickly and cheaply as possible.

Maximum Concentration Perimeter:
- A defensive perimeter suitable for the mid game.
- Turrets placed as close to one another as possible.
- Focus on maximizing firepower.

Battery:
- A group of 4 turrets in a maximum concentration perimeter.
- Each battery is separated from the battery to its left and right by medium electric poles.

If you want your turrets to actually shoot things, you will need a source of ammunition, preferably as quickly and cheaply as possible. The picture below shows a small setup with just one Small Electric Pole, two Assemblers and four Inserters, which will saturate both sides of a belt with yellow ammo made from iron plates.

The output of the ammunition factory shown above is then merged with a belt of coal by means of a T-section, essentially creating one belt with coal and ammo on it. This is called the Perimeter Feed Belt. As the name implies, this new mixed belt is responsible for feeding the entire perimeter. Why is there coal on the ammo belt, you ask? If your base has a power outage, all entities that require electricity to operate will cease to function. In this event, normal inserters would no longer be able to move ammo from the Feed Belt to the Gun Turrets. The Burner Inserter, however, is powered by the coal on the feed belt next to the ammo it gives to the Gun Turrets. This means that a Gun Turret + Burner Inserter combo will continue to operate even without power. As an added bonus, this means that more power is available for your factory.

Now that we have a Perimeter Feed Belt we want to create a cost-effective early game perimeter for our factory. The best way to accomplish this is by placing our Gun Turrets in such a way that every Gun Turret is entirely within the field of fire of the Gun Turrets to its left and right. This ensures that if one Gun Turret is taken out, the perimeter is still entirely covered by the field of fire of other Gun Turrets. I call this a Maximum Dispersion Perimeter. The reasoning behind it is that Gun Turrets are expensive in the early game, and you want to cover as much ground as possible as soon as possible.

Eventually, enemy attacks are going to get stronger. Luckily, your initial perimiter will buy you all the time you need to get your factory set up. Once your turret production and Medium Electric Pole production are up and running, you'll want to start modifying your Maximum Dispersion Perimeter into a Maximum Concentration Perimeter. The concept here is that instead of dispersing your turrets as wide as reasonably possible, turrets must now be as close together as possible in order to combine their fields of fire. Four Gun Turrets form one battery. Each battery is separated by a medium electric pole. This creates a reliable system of measurement that lends itself well to blueprinting once Construction Drones become available.

Once you have a literal wall of guns around your base, you want to commit to adding a wall. It is extremely important to keep one empty space between your wall and your turrets, because more advanced melee bugs have melee attacks that can hit structures behind the walls. You should also be mindful to change the type of ammo that gets fed onto the belt once it becomes economically feasible.

Walls need gates big enough to let a tank pass through without it breaking stuff. To achieve this, simply pick a turret section and remove the burner inserters, then the turrets, and create a gate that slopes back to the same tile axis as the Medium Electric Poles. Make sure that a gate always has at least one battery on its flanks. The combined firepower of two batteries should be enough to keep enemies away from the gate.

It is important that you establish radar coverage of the entire area covered by your defensive perimeter. This will provide you with a live map feed of what is happening in your territory, whilst simultaneously uncovering the Fog of War. It is also important to remember where you placed radar dishes, so add a map marker. Whilst you're at it, also add map markers for gates. The easiest way to do it is to click a radar with the mouse or hit the corresponding key on your toolbar, then observe your minimap whilst it displays the range of the radar. You space them out as much as possible whilst maintaining full coverage in that manner, and hook them up to the power grid by using large electric poles to run a wire to it.

Enemy bases multiply. This includes in your direction. If the enemy bases get too close, they will start shooting your perimeter with Spitter Worms that outrange most defenses available to the player. Artillery guns solve this problem by dropping a one-hit-kill shell on these things. Artillery guns only target enemy structures. This in combination with their range should create a comfortable no-man's-land around your bases. I defer you to Xterminator's youtube video about artillery for further information.

Once you get modular armour, right-click it and slap in Night Vision Goggles, a Personal Roboport, three Personal Batteries and fill the rest up with Portable Solar Panels. Keep 10 Construction Drones in your inventory at all times. This will enable you to build at night, but more importantly, it will allow you to place down pre-saved blueprints and watch as the drones do the work for you. Belt Immunity Equipment can also be slotted to prevent Belts from moving your character, thus preventing miss-clicks.

Making drones construct presaved blueprints drastically reduces the amount of time it takes to build anything and allows for complex shapes, such as Tank Traps. What use are Tank Traps against bugs? As you kill bugs, they will evolve. The larger biomorphs can't fit through the single spaces between the Tank Traps. This makes Tank Traps an effective delaying measure that buys time for your Gun Turrets to take it down. Tank Trap blueprints should not be smaller than 4x4 or larger than 12x12. It should also be noted that instead of tank traps, you can also just make a two-thick wall, but I like to keep the large biters as far away for as long as possible, and Tank Traps offer that.

It is possible to create tank traps that your vehicles can cross by using gates instead of walls. The resulting construction should look like this. Scale up or down as appropriate.

The premise of a pushback supplement for defenses is an old but gold one. Melee biters need to be in melee range in order to bite. So what you do is place roads around your perimeter wall. Firstly, this makes it take longer for the biters to reach your walls. Secondly, this moves the biters away from your walls whilst they stop to bite. You can do this cheaply with yellow belts. However, one could also do it with blue, which is highly entertaining. Now, let us exit the realm of theory and enter the realm of practice. You start by saving a blueprint of belt that is slightly wider than your tank traps. For instance, my tank trap blueprint is 4x4, so my supplement blueprint is 6x6. This screenshot should give you an indication:


Now that we have our blueprint, we apply the supplement over the tank traps, like so:


Belts can not be targeted by biters, spitters or your turrets on purpose, and some would go as far as to argue that a 5x5 belt of blue belt around one's base simply makes it immune to melee attackers.

One could even go so far as to include a reverse set of belts in order to drive the Spitters into the range of your turrets, like lazy pedestrians at an airport.

Due to the relative cheapness of Yellow Belt, Burner Inserters and Gun Turrets, and their independence from your power system, it is also really easy to use your defenses offensively, for the purpose of claiming resources. Once you are able to use the Personal Roboporter, you can rapidly construct a Maximum Concentration Perimeter around resource fields due to the fact that each section, IE the Battery or the Gatehouse, is separated by Medium Electric Poles that are as far apart as possible whilst still being connected. In effect, all you require is three blueprints:
- Perimeter - Straight
- Perimeter - Gate
- Perimeter - Corner

The picture below highlights how this was done to a copper field underneath a bug base. A single line of landfill was used to create a "supply dam" across a body of water. Once that was done, medium electric poles were placed on it at maximum dispersion. After that lines of yellow belt were added. Lastly, underground belts were added to connect the belt lines separated by the medium electric poles. Once the other shore was reached, the belt and the power line continued towards the bug nests, each pole flanked by two gun turrets, these separated from the wilderness with walls. Naturally this offensive siege trench was deployed via saved blueprints laid down by construction drones. Once contact with the enemy was made, tanks were called in to clear the nests off the copper field, after which I plopped down a perimeter in less than five minutes.

Once the bugs have evolved far enough, they will start throwing the big spitter biomorph at you. The big spitter is a ranged enemy who outranges your gun turrets. To counter this, you should modify the batteries of your defense perimeter from 4 gun turrets to 1 laser turret and 3 gun turrets. Do not do this before you get nuclear power. This will lower the DPS of your batteries, but it's better to snipe the enemy snipers than it is to get sniped yourself.


Because they're not belt-dependent, you can also sprinkle them in to reinforce gatehouses, which have less firepower due to replacing their turret battery with a gate and can use a little boost. As an added bonus, the inclusion of Laser Turrets into a Turret Battery will drastically reduce the rate at which Gun Turrets waste Uranium bullets on weak enemies.

Throughout my guide, I have argued that the most important characteristics of a defensive perimeter made out of Gun Turrets fed by a Burner inserter from a single Yellow Belt that supplies both machines is the fact that all of these components are dirt cheap and will not be affected by power failures. The reason why I talk about power failures is that I have seen people lose their main base because they fully transitioned to laser turrets, lost power to their perimeter and were overrun. Sometimes this necessitated a save reload, sometimes the last save wasn't far enough back and it destroyed days worth of effort.

Those memories are the motivation for this guide on early to mid game defenses, but I figured that since power blackouts are such a big factor for me, I should also explain how to efficiently and reliably generate power before you get nuclear power. In this sentence, efficiently entails "Whilst taking as little space as possible" whereas reliably means "using burner inserters to feed coal to the boilers to immunize it to electricity shortages"

I use the system on the picture below, which consists of:
- 2 water pumps (1 per boiler group)
- 40 boilers (20 per water pump)
- 80 steam engines (2 per boiler)
- 40 burner inserters (1 per boiler)


Players are also strongly encouraged to invest in combinations of Roboports, Substations, Accumulators and Solar Panels. The Solar Panels reduce your consumption of coal / oil / uranium. The Accumulators allow you to store surplus energy which is very convenient for laser turret users who suffer from temporary high peaks in power consumption. Below is one example of how such an installation could be done.

Since both the guide and the bonus section about non-electric inserters for steam boilers essentially rely on the concept of non-electrically motivated setups, I felt that I should also share this as it is something in the same spirit. One of the annoying things of the early game is having to run back and forth in order to move resources and fuel around. However, this can be circumvented by means of the screenshot below.

What is happening here is this:
- Burner drill 1 mines coal and outputs on a belt
- Burner inserter 1 gives coal to burner drill 1 to make it self-sustaining.
- Burner inserter 2 gives coal to the furnace.
- Burner inserter 3 gives coal to burner drill 2 which mines iron ore and outputs into the furnace.
- Burner inserter 4 gives coal to burner inserter 5.
- Burner Inserter 5 gives iron plates from the furnace to a chest.

This system will continue running indefinitely, meaning you no longer have to run around with coal.

Another trick for self-sustaining coal harvesting is to point the output of two burner drills towards each other and have a burner inserter take coal out and place it on a belt to other places.

Added in response to ZeroNu's question about how I do corners in a defensive line:

There are a few arguments I can make to advocate for the continued use of gun turrets and burner inserters after the early game and the mid game.

With regards to gun turrets, laser turrets do not just consume energy when firing. They have a continuous power drain. If you want a lot of laser turrets, that's going to mean a lot of passive power drain even when they're not shooting anything. It might seem small at first, but it will add up in the end.

With regards to burner inserters, they only consume energy (in the shape of a combustible block) when they are moving ammo from the belt to the gun turret. In contrast an electric inserter not only has a continuous power drain whilst passive, but also requires additional energy when moving ammo from the belt to the gun turret, and like the laser turret it ceases to function altogether when there is a power outage. On top of that, burner inserters can operate on a plethora of resources. Want to get rid of all the wood you've accumulated by clearing forests? You could put it in a chest and shoot the chest, but you could also put it on this ammo belt as fuel for your burner inserters. Or think about the fact that once you enter the Nuclear age, you can still use any coal or solid fuel that you get your hands on for these things.

Lastly, I want to talk about human error. Even if you yourself know what you are doing, you can not control the actions of other humans, nor magically impart your knowledge upon them. That means that in a multiplayer game, as we all know, accidents are bound to happen at times. The main risk with laser turrets, I find, is not running out of power, because a veteran player usually counters this in a timely manner. The main risk with laser turrets is that all it takes to disable your defenses is one idiot driving a car at top speed in your base hitting an electric pole to cut some, if not all, of your laser turrets off from the base's electric grid. In contrast, the gun turret + burner inserter combo is like the AK-47 of base defenses. It might not be the fanciest thing out there, but it is cheap and it will never let you down as long as there's ammo and combustibles on that belt, as idiots can't break belts with vehicles.

With that said, I thank you for reading my guide and wish you happy camping.

My thanks go out to the following people for providing suggestions and reminders:

• Armyof19 for reminding me to include the pros and cons of laser turrets.
  
• ZeroNu for reminding me to include how I do corners in a square base defense grid.
  
• Coffee Daemon for reminding me to include the benefits of solar banks and accumulators for defenses (example, for coping with laser turret bursts)
  
• Dio Brando for suggesting the use of gate tiles to create tank trap fields that can be traversed by the player's vehicles.
  
• Detoxifier for reminding me to include the use of belts to push enemies away from the player's walls.
  
• JKS-Joe Blake for suggesting the use of reverse push-back belts to drive spitters into turret range.
  
• PirateBear for bringing an incorrect sentence in the closing remarks to my attention.