In-Depth FOB guide for all skill levels.

-WHY WOULD YOU WANT TO DO FOBS-
For cool stuff. Newer players can get all the unprocessed materials they want. Experienced players can do it for lots of processed materials, plants, S+/S++ soldiers, or just for high espionage scores. It is a never ending dearth of not-quite-the-same content that will keep you going when you realize this is the last Kojima Metal Gear.

-WHY SHOULD I LISTEN TO YOU-
I have played about 800 hours of just FOBs, and at one time I was top 25 worldwide in espionage ranking.
http://imgur.com/aRkkl8V

-HOW DO I GET LOTS OF X-
For unprocessed materials just look for a low level (or high) FOB and invade the Base Development platform. When you pick the place you want to infiltrate you can see a little window to the right side of the screen that tells you what you can find on the FOB such as defenses, traps, security, stats of guards, and containers. You want to pick the one with a large amount of materials in that little window.

For processed materials you want a high level FOB. On the bottom left of the screen where you pick which platform to infiltrate you can see a potential rewards screen. Each platform gives different rewards for successfully infiltrating the core of the FOB. The Support Platform will reward the most processed Fuel Resources, Base Dev will reward the most Minor Metal. For plants, pick Medical Platform.

For good soldiers you want to invade any of the platforms (some say that Command Platform is best for this) that is over level 40. The higher the level the higher the chance there is that you will be awarded volunteer S+ and S++ soldiers, this is a pretty consistent way to farm levels for your own Base Staff, as the only other ways to get them is to complete the main game, do online dispatch missions, or do FOB events which will be explained later. Sometimes you will get lucky and see some poor schmuck has left S+ soldiers in his Defense Unit, in which case you should fulton every single one of them and pray they don't counter-invade and steal them back.

For espionage points you want to pick any high level FOB, the higher the better, and stealth it to the best of your ability with the weakest soldier on your combat unit with all-around stats or at least one that will hit the magical x2 point modifier. You get bonus points for not using reflex, not killing guards, not going on combat alert, sneaking during the daytime, and killing Defenders. Soldiers with the Climber or Gunman(if you use reflex) traits are the ones to look for. There is no tangible benefit to doing this other than being the best. If points don't matter to you just use Snake.

-WHAT CAN I EXPECT TO FIND AT A FOB THAT ISN'T LOOT-
Once you have picked the reason you are invading someone else's hard earned FOB, you need to know what comprises the defense of the FOB in question.

[Guards]
Self explanatory. They defend and patrol the FOB just like any soldier in the single player game. The higher the stat of the soldier the better they will be at spotting you, choosing whether or not to investigate, speed of investigating, hearing range, and how much damage they can take before dying. The better equipment you have in single player, they better equipment they will have on the FOB. Combat Armor, Stealth Suits, Helmets that deflect shots, and how powerful their weapons are, and what kind of weapons they have available, are all determined by what you develop in single player. If they spot you, you will go into reflex mode (if you have it turned on) and if you don't incapacitate them by killing, knocking unconsciousness, choking, diving and then holding them up etc. They will start a Combat Alarm. A good rule of thumb is: guards will always investigate a magazine, or a tranq dart hitting a surface at least once without using the radio to notify CP. If you shoot at them with any other gun, stun or lethal, they will react as if being shot at and radio in to CP.

[Cameras]
Self Explanatory. Weak to all lethal weapons with very little health. They will cover an area of about 20m in front of them with a 60° cone that will swivel left and right covering a total of 140° or so. They have a blind spot directly under them and parallel to the wall they are placed on. If you destroy a camera CP will send the nearest soldier to investigate. 99% of the time this will end in the FOB going on Alert. Guards can also hear the camera explode when you shoot it, around 25m radius depending on the guard. As you upgrade them they will be able to swivel faster, and on Lethal FOBs you can upgrade them into Gun Cameras that have an assault rifle built into them. Ironically this upgrade makes the gun camera swivel slower than the lowest upgrade of the regular Camera, but depending on how you stealth this can be a good or a bad thing. The best way I found to avoid being spotted cameras is wear squares camo and go prone, they will usually ignore you or stop noticing you even if you are right in front of them and least more than 5-8m away Warning: this does not apply to player placed cameras. As far as the gun goes, it tickles even wearing fatigues, but not something to be overlooked. As your Unit levels get higher, players will be able to develop a tool that allows them to place a camera in a spot of their choosing, it can be on any just about any surface, even flag and light poles.

[MINES]
Whether player placed or static, these anti-personnel mines are a pain. When placed they will trap a 3m 90° cone with the explosive being in the middle, Static mines (hence the name) are always going to be in the same spot on every FOB. Player placed mines are self explanatory, they are where the player places them. If you set a mine off, and if any soldier hears it (usually the entire strut) it will cause a soldier to kneel and radio in to CP, which will in turn make CP send soldiers to investigate the source of the explosion ending in the FOB going on alert. If you are infiltrating a non-lethal FOB the claymore type mines will be replaced with LLG mines, which have a short circular trigger radius and it will only knock your soldier unconscious. LLG mines are also silent.

[Infrared Sensors]
Gates that block off sections of the catwalk. A time waster mostly as you can just hang off the ledge or drop to a lower catwalk and bypass it completely. If you trigger one it will cause CP to send a guard to investigate. If you destroy a Sensor, a guard will investigate and will probably end in the FOB becoming alerted. As a player upgrades their Sensors it will add more beams to the gate, as some enterprising intruders have found reliable ways to dive through lower level Sensors.

[Antitheft Devices]
A small circular device that will set off a localized alarm that will cause CP to send a soldier to investigate, and alert every guard that hears it if you fulton something in its protection radius (even guards.) As a player upgrades their Antitheft Device it will increase the area in which it can sense something being fultoned, and eventually be able to sound its alarm just by the intruder walking near it. If you are unsure if they possess upgraded AT Devices, just give them a wide berth. You can destroy them but it is risky as it is about as loud as destroying cameras.

[UAVs]
Floating cameras with guns on them, these annoyances patrol the perimeter and bridges of the outer struts and, depending on which platform you infiltrated, the inside of buildings too. A UAV will usually have its camera and gun facing in the direction of where it is currently moving, then point it at the FOB when it stops. More durable than the simple camera. UAVs have a weak spot where their camera is located. Unlike cameras and gun cameras, if you destroy one it WILL NOT automatically alert CP. During combat alarms their guns do decent damage and sometimes UAVs from other struts will join in on shooting you. When you destroy it, it will fly in a usually outward direction from you, and hopefully splash into the water and not into the strut itself. Guards can hear when a UAV is destroyed it has a similar range of a guard hearing when you destroy a camera. If the guards don't hear you destroy a UAV, they will definitely hear it if it flies into one of the struts; It's about as loud as a mine going off. The best way I found to avoid UAV's is to wear squares camo and go prone, they will usually ignore you or stop noticing you if you are more than 5-8m away. UAVs have a tendency to, when destroyed, crash into other UAVs if they are close enough. This happens enough to make me think Kojima made them do it more often on purpose. Non-lethal UAVs are similar to above but will shoot smoke at you, stunning you and obscuring your vision. A nice bit of TECHNOLOGY is that you can choose where to shoot the UAV and it will determine where it spins off when it blows up. Shooting the UAV on it's left side (your right) will cause it to spin off to the left and shooting it on it's right side (your left) will cause it to spin off to the right and hitting it dead center but not on the weak spot will cause it to fly straight back.

[Gun Emplacements]
Heavy machine guns, "anti-air" cannons, and mortars. 95% of the time these will only be used against you during combat alarms and from other struts. Non-lethal bases will launch sleep-gas mortars at you. Mortars can also be used to shoot flares that light up the sky around you that last a long time and they can fire several. This happens during and after combat alarms.

[Decoys]
Same thing you find in single player. They look obviously different from the guards if the guards are wearing combat armor or the stealth suit. Be careful of popping them on high level FOBs as they are likely shock decoys that will knock you out if you pop them while standing near them not to mention guards can hear them, and send the FOB on alert.

-WHAT KIND OF GUARD DEFENSES ARE THERE-
When you go to look at which platform you want to infiltrate, you can see a little gun icon on the far right info screen. It will either be a shotgun(Short Range,) an assault rifle(Mid range,) or a sniper rifle(Long range).

[Short Range]
Guards will be equipped with shotguns, ballistic shields, and SMGs. Shotguns will knock you prone depending on how far away you are from them. Shields deflect shots from the front during a combat alarm, or from the back any other time. With practice and knowledge you can easily cheese this type consistently by crouch walking, using a stun shotgun/sniper rifle, and reflex mode.

[Mid Range]
Guards will be equipped with assault rifles and LMGs. These hurt and will deal consistent damage to you from short and medium range. With practice and knowledge you can easily cheese this type consistently by crouch walking, using a stun shotgun/sniper rifle, and reflex mode.

[Long Range]
Guards on roofs and towers are equipped with sniper rifles. Every other guard is equipped with assault rifles. These are the most common type of FOB you will see at mid/high level and by far the most challenging. The reason being is that if a FOB becomes alerted to intruders, EVERY SINGLE GUARD THAT IS ON A ROOF OR A TOWER WILL BEGIN SCANNING THE AREA THROUGH THEIR RIFLE SCOPES. What this means for you is that all those guards have expanded their sight cones by about 10 times more than the other two types of FOBs. Worse yet, guards can hear certain weapons even while suppressed even if they can't spot you. Normally this means a guard will look in your direction and probably investigate the noise. Unfortunately with guards equipped with sniper rifles, when they turn to face the noise, they are looking through their scopes as well and will probably spot you instantly. Even worse, sniper guards can spot you from ENTIRE STRUTS away. EVEN WORSE, sniper guards can fire a shot at your character AS SOON AS REFLEX STARTS, what can and will probably happen is that you get hit, knocked down by the shot, and your reflex mode is wasted. Even if the shot misses they will probably out range your weapon. And for the final bit of bad news: if a sniper gets off that shot in reflex, it causes all the other soldiers to look your way, this will usually mean that you will be double fucked as all the snipers on the strut are now looking your way and you unable to take them out before the combat alarm is sounded. "FOR GOD'S SAKE WHY???" you ask? Well, there is hope. If you don't alert the base to an intruder then they won't scope up, and will continue act like every other guard. Much easier said than done.

-WHAT IS THE DIFFERENCE BETWEEN LETHAL AND NON-LETHAL FOBS-
Lethal is just that. They will stab you with bullets if you get caught. It hurts. If you aren't playing as snake, and your soldier isn't under Direct Contract your soldier will be KIA and permanently gone from your roster.

Non-lethal is the same thing but instead of dying you will get knocked unconscious and have to do a little QTE to wake up faster. If there are any guards nearby they will attempt to fulton your character whilst unconscious, if you aren't playing as snake, and that soldier isn't under Direct Contract the Defender will steal your soldier with no way to get him back unless the Defender counter-invades and then you counter-invade back.

-HOW DO I GET STARTED AT INFILTRATING FOBS-
Just do it!

[Weapon Choice]
First you need to decide if you want demon points or if you want to be nice and not kill another player's hand picked men.

If you want to go lethal you can bring a high * sniper rifle for all your anti-personnel needs, one shot will put them on the ground in a fetal position waiting to die or at the very least knock them down. Depending on the sniper rifle and how good the armor is on FOB guard, a 7* sniper it will take 1-2 body shots to kill a guard outright. The AMRS sniper is my personal choice though you may want to bring a Brennan or some say a M2000 to guarantee those 1 shot body shots. With enough practice a bolt-action is not as much as a malus as it seems at first, though you may find it a bit lacking when you need to put down more than one guard at a time.

If you want to go non-lethal then the 7* S1000 Stun shotgun is the best way to go. It can knock out soldiers with one body shot out to 30m, and you can customize it to have a 2nd rank suppressor on it.

If you are infiltrating lower level FOBs and the guards don't have armored helmets yet, you can pretty much use whatever you are comfortable with.

You will usually want to bring a tranq gun of some kind be it sniper or pistol. The reason is its a nice backup if you decide to bring along a stun shotgun as well. The most important reason is that the game considers tranq darts to be like empty magazines. If you fire your tranq gun at a wall near a guard it has the same effect as if you threw a magazine in the same spot. Very useful as it more accurate and faster than pulling out your empty magazines.

If you are playing as snake you can bring either the Hand of Jehuty for tactical guard disposal, or the max rank Stun Arm for knocking out half a platform with its level 3 charge.

[Armor/Camo]
You have to decide if you want to plan for the worst, or plan for the best. Sneaking in Combat Armor is not that bad if you get used to it, you will almost certainly alert the FOB, but it will give you some much needed protection against the defender's minions.

On the other hand, wearing Squares fatigues will make you a complete camo ninja. You can prone-roll as close as 15m at night in front of a guard and he won't spot you. Be aware that you are made of paper whilst wearing fatigues, and even 1 UAV can take you down quickly

The fully/almost fully upgraded sneaking suit is a nice compromise between armor and camo index with the added benefit of near silent footsteps also great for purposefully going up against defenders.

[Other Items to Bring]
Noctocyanin, 1* Frag Grenades, NVGs, Box, Smoke Grenades, Sleep Grenades, and an empty slot to pick up D-mines and LLG mines

[Practice]
Do the EVENT FOBs, they will give you event points which you can cash in for camo, emblems, colors, new items and S+/S++ soldiers. The downside is other than guards they aren't very representative of the FOBs you'll come across online and some events are very very grindy if you want everything.

Find a player with the level of FOB you want to practice on and support them. You can train on their FOB for free, but you won't win anything doing it this way, you won't lose anything either.

Find an FOB you want and go to town on it. This will give you much needed practice and tangible rewards at the same time. The downside is if you blow it you are giving a bunch of people free wormholes to attempt to steal all your stuff.

Attempt a security challenge. This is a useful alternative if you want the real deal but don't want to accumulate revenge wormholes. Security challenge lets you attempt a FOB like normal except you get more rewards, but the Defender and his supporters  will always know you are there no matter how stealthy you are. I can't speak for other consoles but on PS4 maybe 1 in 20 times a defender will actually show up, so this may be a good alternative for practice and for real.

-HOW DO I FIGHT DEFENDERS-
You don't. Unless you like wasting your time you can only lose slower. The advantage is completely stacked in favor of the defender. Try to have fun with it but know you are going to lose 90% of the time and there is little you can do about it.

-HOW DO I STEALTH BETTER-
As stated earlier, the best way to tackle high level sniper FOBs is to not make the FOB go into alert mode at all, this requires near perfect stealth. You will need to have a good understanding of all the mechanics of interacting with unaware guards. Use magazines, tranqs, squares fatigues or its like, use the catwalks and the sides of platforms as much as you can rather than going on top of it. Experiment in training and security challenge as much as you can to figure out how guards react to you, what they do, etc. I try to explain as best I can in the guide here, but practice and experience trumps all.

[STEALTHING GUARDS]
Guards have three loose "states": At Ease, Alerted, Combat,

At ease: The default state. Vision is reduced, Hearing is worse(not confirmed). Will slowly patrol around their part of the FOB. Patrols are usually the same everywhere since most people don't edit them in the security settings. Once noticed (white semi-circle on the HUD) it is usually better to roll away from them if you have the camo fatigues for it. Once guards are alerted they will never go back down to at ease for the remainder of the infiltration.

Alerted: When this state occurs guards have increased vision distance and better hearing. Snipers will begin scanning the area through their scopes. They will investigate quicker and run to where CP tells them. There is a sub section of Alerted where guards will believe they are under fire and direct their attention to where they think they source is and shoot at it as well, sometimes this means guards will be a full run straight ahead but looking at their left and run right by you. If not being told to run somewhere by CP they will usually be stationary. Less likely to investigate empty mags/tranqs.

Combat: You should know what this looks like. Not the end of the world even if you are wearing fatigues. If you trigger a Combat Alarm your next immediate goal is break line of sight between guards, UAVs and you, then move away from the place where they last saw you right away. Soon after, a guard will call for a cease fire, radio CP, and 3-5 guards will come to search the area where you broke line of sight. Once they have searched the immediate area where you broke LOS, they will radio CP saying they cannot find you, then the Combat phase will go away and be downgraded to Alerted Soldiers will continue to search the immediate area beyond where you broke LOS but you will at least be able to go into Reflex mode again if that is your thing. If you are playing at night they will use mortars to launch flares that light up the strut and are devastating to your camo index. Although rare sometimes you can trigger an infinite combat alarm by knocking out a ton of guards during the alarm that WOULD have been the ones the game assigned to call the cease fire and search for you. Because of the rendering priority the game won't replace those guards and the combat alarm will never end. You see this a lot if you get caught on the same strut more than say 3 times. If the combat alarm has been going for more than 4 minutes and you haven't been shot at since it started it might be bugged.

Using Reflex Mode is not necessary to do FOBs. I personally don't use it in single player but use it a lot in FOBs, but if you are not playing for points or fighting defenders there is no reason not to use it as it only helps you. To each his own.

[FINDING YOUR ROUTE]
There are hundreds of videos on youtube showing all different kinds of ways to do FOBs, showing different routs, different strats etc. I'm not going to go into the different ways, but you should always be looking for the path of least resistance and be able to adapt on the fly. The beginning of this video is one I like to use a lot because you can avoid all the guards on the strut if the strut is the right configuration.
https://www.youtube.com/watch?v=xc78_Bi9oAM
Cameras and UAVs are easier to deal with than wrangling guards with magazines though sometimes you may not have a choice.

FOBs aren't always the built the same, someone's 4/4 support platform may not be the same as your 4/4 support platform. This is largely dependent on the waters that the defenders have bought. A good rule of thumb is go for the FOB that is the highest level that ISN'T the first FOB, though sometimes the first FOB is the only one that is appealing to infiltrate.

[HOW DO I GIT GUD]
So you have hit the upper limit of your skills but you want to crack open level 59 sniper FOBs and steal everything not nailed down? Here are some tips:

Use your tranq darts and empty magazines. You can always distract a guard at least once before they radio in and set the base on alert.

You can go prone in front a camera/UAV wearing camo and it won't see you, same thing if it already has noticed you. Works 8+ meters away. This does not work with Player-placed cameras.

If you get spotted at close range, you can dive into a guard and aim at him to hold him up. This is quieter than shooting them with a stun weapon. Pop him in the face with a tranq and hide his body after that.

To guarantee a kill on someone's guard, throw them off the FOB. This is also great for hiding unconscious guards.

You can use 1* Frag Grenades to distract alerted snipers away from your route, it usually won't kill a soldier by accident. Works great if you are wearing camo and there are white sniper icon/detection thingies on your HUD.

if a Long-Range FOB is alerted you can try to take out as many snipers as you can from the previous platform.

If a sniper FOB is alerted don't fire your sniper/shotgun/ass rifle where a sniper has/or could have line-of-sight on you. Fire from behind walls and large pieces of cover.

You are invisible and immune to FOB defenses save for gates for the first 5 seconds of spawning in. (Guards can still hear you though.)

Always be on the lookout for user placed mines and cameras, some people aren't retards and know popular routes. They are the most dangerous aspect of high level FOBs.

Roll across or under bridges.

Always keep a lethal weapon (like a sniper rifle) at the ready. It doubles up at taking out guards and cameras/UAVs.

Don't hop the support strut catwalk onto the garden staircase until you git gud.

If the base is already alerted, then you don't have to worry if guards hear you shoot all the UAVs. Exploding UAVs are also a great distraction.

You can place marks on enemies through walls that you can see with Nocto pills. This appears to be an exploit and might get patched.

You can press Square/X to switch to your pistol slot and vice versa while aiming.

If an FOB has S+/s++ soldiers on the defense team they will be put on the final platform first with more being added outward.

Be patient.

Climbing up ladders and pipes and standing in/under lamps wrecks your camo index.

The Defender will only know an intruder is there if the FOB is on alert or has an S rank Intel Team.

Be especially careful of player placed cameras that are near face level. Usually if they notice you there is no way to avoid being spotted except by destroying the camera, even if you are wearing square fatigues.

You can charge your Stun Arm while prone, or even while rolling!

If you shoot a UAV on its left side (relative to you), it will spin off to your left, and vice versa, giving you limited control over where you want the UAV to fly once yous shoot it, whether into the sea or into the strut.

If you want to preserve your no kill bonus but for whatever reason a guard is in the fetal position and is about to die you can knock them out and fulton them to keep your bonus

If you fire your shotgun while then immediately stop aiming you won't rack the shotgun, if you reload before aiming again you can skip racking the shotgun completely. This strangely does not work with bolt-action sniper rifles.

Prone roll > Crouch walk

R&D soldiers and all females can't get the unit medal from being rescued from the core of an FOB during a counter-invasion.