Had a rad roach infestation and one roach would not die it killed 5 armed dwellers

This has happened to me twice so far, first one wiped out 20 armed dwellers, this time 15 just started moving everyone out of the way hoping not to die. Killed the rest of the group but one roach would not go down. It's why I deleted my first vault.

How much firepower did you have to combat these rad roaches?

Have been wiped out 3 times today, got down to one roach, then it killed 15 to 20 dwellers with sawn offs and hunting rifles. I used 25 stimpacks to keep them going. Then just moved everyone out of the way to keep from being completely screwed. Is that enough, or do I need to find something better to deal with the most basic enemy in the game?

I've had this one. Rad roaches killed 75 people, levels 15-35. All decently armed. Lowest weapon was a hardened sawed off shotgun, highest weapon was an enhanced flamer.