What Atom Requires is a holotape in the Fallout 4 add-on Far Harbor.
Location
The tape can be found in the pump control, on a table.
Transcript
DiMA: I have to say I'm surprised. I had assumed you and your followers would be more adamantly hunting for the sub's launch key.
Confessor Martin: I hope we haven't disappointed you too greatly. I'd hate to anger our landlord.
DiMA: I believe I'll survive. But am I mistaken? Does your god not require you die in a nuclear blast? Is that not why you've taken up in the Nucleus?
Confessor Martin: It's not a transaction, DiMA. Atom requires nothing of us. He has granted us a chance to become something greater. To Divide our weak mortal frames and bring life to millions of new worlds. We are simply accepting the opportunity His Glow presents, whatever form it may take.
DiMA: So if you found the launch key, you wouldn't use it?
Confessor Martin: That... I don't know.
DiMA: Are you afraid?
Confessor Martin: I'd be mad to say I wasn't. But... we've made a home for ourselves here. Friends. A family.
DiMA: A place you belong.
Confessor Martin: Exactly. The Nucleus, it is a blessing of the truest order... it would be hard to leave such a gift, even if it is for another. But, regardless, the key is lost. So until Atom sees fit to return it, I'd dare say you're stuck with us.
DiMA: I believe I'll survive.
