So many deathclaws... How do I make them stop?
I've noticed that deathclaws tend to attack right after a new dweller joins the waiting line outside my vault OR right after I let someone into the vault from the waiting line. They don't seem to attack randomly while nothing else is going on.
To answer your specific question:
How can I stop all these deathclaws from eating my dwellers, while still attracting new ones?
You can't stop them
You can stop them from coming by not clicking on the radio room (so no one gets added to the line outside the vault) and by never letting dwellers in or out of the vault (so the door never opens). Obviously this is not really feasible as it prevents you from adding fresh blood to your vault and from getting the weapons you need to defend it.
In case you thought lunchboxes would be your savior: sorry. Dwellers from lunchboxes don't bring deathclaw attacks when they join the waiting line, but they can still trigger an attack when they enter the vault. I haven't done testing to determine if there is a lower percentage chance for lunchbox dwellers, but I have triggered a deathclaw attack when I brought Bittercup into the vault.
But you can resist
You can minimize the damage that the deathclaws cause by arming all of the dwellers in the topmost levels with the best weapons and outfits you have. Posting guards in the vault entrance is also helpful. Your goal is to have each room wear the deathclaws down as they go deeper into the vault. The deathclaws move from room to room fairly quickly, so manually sending a dweller with the best guns to chase them down is difficult. You can try sending the defensive guys a few rooms ahead of the deathclaws to wait for them, but equipping the the dwellers assigned to the room with guns is faster and should have better results.
Plural of anecdote is data, right?
Some facts from personal experience:
In my fancy vault with 150+ dwellers and Mr Handys, the deathclaws will be killed on the second or third level down. In that vault, everyone on the top floors is carrying weapons that do 10+ damage per hit, and the deathclaws still get past vault entrance, top floor room (with 6 dwellers), and one or both of the second floor rooms before dying. No one dies when this vault is attacked, but they whine about the damage they took.
In my not so fancy vault with 100 dwellers, everyone on the top floors is carrying rifles or better (so minimum 5 damage per hit on most of the second floor and third floor, min 6 damage on the topmost floor). Deathclaws here will get through the top two floors with ease, start to die on the 3rd floor, and be finished off on the fourth floor. After the last attack I had to revive three dwellers and pass out all 25 stimpacks. The deathclaws also stole/drainined/rekt about half of my water/power/food resources. This was a pain in the ass but not as difficult to get out of as the early vault death spiral.
tl;dr:
Don't let anyone in or out of the vault; don't let anyone line up in front of the vault. Complain to Bethesda so that deathclaws will get nerfed in the next patch.
I have found that if you cause an incident by rushing a room right as you open the vault door to let someone in, deathclaws do not follow afterwards. This has worked the 3 times I've tried it. Rats are much easier to kill than deathclaws. Best of luck.
Train in endurance BEFORE leveling. ((HP only grows while leveling and is based on END) Training END after leveling doesn't boost HP at all, only radiation resistance.) Wear endurance suits until fully leveled, and send people out into the wasteland to level quickly (with a full supply of 25 Stimpacks), Radaways are less important, because at over 10 Endurance, their explorer journal will occasionally say "took 0 points of radiation damage." (you can give them a few to be safe, but radaway doesn't really matter, save it for water shortages(which might happen if most or all of your water pumpers are temporarily out in the wastes leveling up).
Aside from that, once someone's at level 50, put them in good clothes, and arm them well. That part will be easy, because with all the exploring you've just done for the leveling, you'll also have a good stash of special armor and weapons.
After that, Deathclaws (and those dreaded molerats) will be a minor issue. As for raiders and roaches, they'll pretty much melt away like butter in the microwave.
=D
Deathclaws do appear before you have 60 dwellers, just only in hard mode. If you train all of your Charisma dwellers with maxed out Luck and place them in the Radio Room, that will stop the Deathclaws. Yes, it's true. Max Charisma and Max Luck (you can train them up to 10 and then put outfits on them and that will increase their stats even more). You cannot "turn off" the Radio Room, even if there aren't dwellers in it you still have a slight chance of being attacked by Deathclaws (surprised me too).
Deathclaws won't show up if you have less than 60 dwellers in your Vault (60 exactly may also be okay). So, aside from never opening your Vault door and never using the Radio, one possibility is to send of your less productive dwellers out into the wilderness and let them die (or just remove some of the dwellers killed in Deathclaw attacks) until your total population is 60 or less.
It's worth noting that rooms you've unlocked stay unlocked even if your population takes a dip, so if you are careful and callous, you can raise 40 dwellers (assuing you are already at 60) and then as soon as you have 40 kids, start sending the "Doomed" generation out into the wastes to die. You'll get a lot a Deathclaw attacks, especially opening the vault door a mess of times, but eventually you'll be safe again, with all the rooms unlocked.