Protecting your settlement is a complex affair. The primary goal is ensure that they can defend themselves. The secondary goal is maximizing the defense stat, to minimize your settlers' exposure to raiders. To be on the safe side:
- Build defensive structures to increase the defense rating. Note that turrets are autonomous, but larger ones require power to function. Guard posts don't require power, but on the other hand, they need to have a settler assigned to them to generate defense.
- Placing turrets and guard posts with snipers in elevated positions will make it harder for melee enemies to get to them and provide clearer lines of fire. It can also help against grenades.
- Equip settlers with whatever surplus guns and armor you have. Even a flimsy pipe pistol is better than nothing.
- Companions who aren't accompanying the player will assist the settlement they are at if it gets attacked. Assign companions to settlements accordingly.
- Players with the Automatron DLC can build robots to help defend settlements. They can be left to roam or assigned to a guard post the same way as a settler.
- The game generates attacks on settlements in two ways:
- It generates Defend Settlement missions for one of your settlements.
- There is a chance for an enemy attack to spawn every time you visit a settlement. That means settlements you visit often will get the lion's share of attacks.
- Having a defense rating equal to or greater than the sum of a settlement's food and water will prevent attacks from raiders entirely, according to the game's settlement tutorial. This way the player can choose to have some settlements get weapons and armor and others that get none but have a sufficiently high defense rating. This only affects Defend Settlement missions, not enemies that spawn from player visits.
- To see what a settler looks like holding a particular weapon, give them the weapon and then assign them to defense. When they go on duty they will draw the weapon and look down the sights for a few moments. Note that settlers assigned to defense are not always on duty.
- Raiders who are killed by settlers can be looted, even if the player was not present during the battle.
- If the player builds a siren near a guard post, the guard will activate the siren upon spotting an enemy. The siren will alert settlers in the area that enemies are approaching, and they will move towards the siren to help defend. Wandering settlers can also activate a siren, but there's no way to be sure anyone will be there.
- Multiple sirens can be daisy-chained to alert larger areas, but testing is needed to determine whether distant settlers move towards the enemy or just towards the nearest siren.
It's a good idea to equip settlers with whatever surplus guns and armor you have.
Newly recruited settlers start with a random unmodified weapon based on the level range of the area their settlement is in. Since Sanctuary is in the lowest level range, all settlers there start with unmodified pipe pistols.
- Settlers do need some ammo for their guns. Unlike companions, settlers do not use up their ammo; they just need some in their inventory. Testing indicates that as long as they have the necessary ammo in their inventory, they ignore its consumption entirely.
- It would have been cool if Bethesda had made it so that ammo respawns as they use it, in which case giving them enough ammo for one full magazine would be necessary to avoid having to reloading prematurely. This would have been somewhat more balanced.
- While equipping settlers, keep in mind that they do not use VATS and they do not use stealth, so any armor mods that add AP or improve stealth will not benefit them.
- Bayonets are a good option on long range weapons in case the settler gets rushed by an enemy. Shotguns and pistols/revolvers function well at melee ranges so they don't need one. Alternatively, settlers can be given a second, unequipped melee weapon, which they will switch to if an enemy enters melee range.
- Settlers don't seem to benefit from night-vision scopes, so regular scopes serve them just as well.
- In addition to armor and weapons, it's a good idea to maintain a stockpile of things like Road leathers since most of the clothing settlers come with doesn't work with a full set of armor.
- The enemies a settlement will face is based on the level range of the cell the settlement is located in on the map. In general, settlements located further south will face tougher enemies.
- The level the player is at when first visiting the cell a settlement is located in (it doesn't need to be the settlement itself) may also play a role in determining the level range of the enemies.
- When looking at weapon damage, keep in mind that settlers do not have perks.
- Settlers often sit back and fire short double-barreled shotguns at enemies from range. This tends to make the weapon ineffective unless the enemy closes the distance themselves. There's no way to tell settlers to engage at close range, so it's best to only equip settlers with double barrel shotguns with long barrels.
- Since they don't need ammo, settlers can make good use of the Submachine gun.
- Giving a salvaged Assaultron head to a ghoul settler is an option, since ghouls are immune to radiation.
- Extensive testing indicates that settlers always use hip-fire, regardless of whether the animation shows them looking down the sights or not.
- Testing indicates that settlers are either unaffected, or else barely affected, by recoil.
- Reportedly, when using scopes, settlers only use the accuracy stat. The zoom has no effect on them. Therefore one of the long scopes provides them with the most accuracy at all ranges, not just at long range as it would be with the player.
- Settlers with recon scopes will add target indicators to the player's compass, just like when the player uses them. Having at least one settler with a recon scope at each settlement can be quite helpful. It presumably may also provide other settlers with the target's location, but this cannot be tested.
As a result, the best mods for settlers are quite different from what a player might choose. In general:
- Light barrels work the best, due to points 1 and 2 above.
- Short light barrels have the very best hip-fire accuracy, and seem to be the best choice for automatic weapons. Also a good option for semi-auto pipe pistols.
- Long light barrels seem to be the best choice for bolt-action and semi-auto rifles.
- For laser/plasma weapons, an improved short barrel with a fine-tuned beam focuser provides the most accuracy. A sharpshooter's grip, when available, will provide a small additional boost. A sniper barrel provides higher damage and longer range in exchange for lower accuracy. Automatics are also very effective, and the barrel choice is obvious there.
- An automatic beam splitter can be very effective at shorter ranges since settlers do not experience the effects of recoil. However, the risk of friendly fire is immense. They also tend to fire at ranges that render the weapon ineffective due to the scatter. Fun to mess with, but not necessarily recommended.
- Long scopes are the best choice for all weapons, regardless of the range used. When long scopes aren't available, use whatever provides the highest accuracy.