The Nucleus

The Nucleus (formerly Mount Desert Island Naval Facility) is a pre-War United States Navy submarine base, and after DiMA made it his home, allowed the Church of the Children of Atom to settle the location. In return for the new home and center of worship, they agreed to protect his old memories from being accessed.

Background
The Mount Desert Island Naval Facility still houses the derelict USS Democracy in its dry dock. While there for repairs and refitting the submarine's reactor was sabotaged by the captain, Arnold Wabash. With the Democracy's nuclear reactor leaking radiation, its crew and captain were recalled while hazmat teams worked around the clock to clean the facility and make the submersible usable again. However, the process would take weeks to complete. Admiral Edward Grath suspected foul play and informed Captain Wabash that he would file the court-martial personally if he was responsible. The personnel of the base survived the nuclear bombardment, and so would the admiral, but not the captain.

Following the Great War, the facility lay idle, its radiation keeping people away, until around 2178. After DiMA landed on the Island, he found the facility and made it his home. Sometime later, Faraday joined DiMA, and, after the Church of the Children of Atom was exiled from Far Harbor, the congregation led by Confessor Martin were guided to the facility by the Mother of the Fog. Brian Richter: "Hmph. You're back. More than I expected. Did Atom reveal something to you?" The Sole Survivor: "I drank from the spring and a woman led me to this icon. Does this mean something?" Brian Richter: "A woman? Led you to that icon? What woman? What did you see?" The Sole Survivor: "Is there something special about this thing?" Brian Richter: "I think it may be a message from someone very important. So I need you tell me what you saw." The Sole Survivor: "It was... otherwordly. The woman, she was like a living shadow, cloaked in mist." Brian Richter: "Atom above. You really did see her. The Mother of the Fog. The Mother is a messenger from Atom. Acts as a guide to those important to His plans and the future of this family. She's the one who led the first of us to this place. And if she revealed herself to you... then I'd say the path He's lain for you is clear. If you are prepared to take the next step, then I believe there is a place for you among Atom's children." The Sole Survivor: "So what exactly happened to me at the spring?" Brian Richter: "Seems Atom granted you a vision. Only those deemed worthy of joining the Children have them... and live. But for some rare souls, he sends... more. A messenger. Or in your case, the Mother." The Sole Survivor: "So was the Mother real?" Brian Richter: "Most believe she's some sort of spirit, a creature of the wilds, though a few claim she's just an old hermit. Regardless, our family wouldn't be here without her. If she figured in your vision... well, there are few signs clearer you're meant to be one of us." (Richter's dialogue) Afterward, DiMA departed to found Acadia, leaving the base in safe hands. While there, however, DiMA used the base's computers to expand his limited storage capacity, offloading the oldest memories into the pen's data banks. For their new home, Confessor Martin agreed to guard his memories.

Layout
The facility exterior, made almost entirely of concrete, is built into the side of a mountain. Upon entry, there are two doors on the left that each lead to a locker room. If one continues down the hallway, they will arrive at the base. On the right is the Vessel, a pre-War submarine.

Continuing forward through a wooden shack, there is a wooden ramp up. If one goes up, they will arrive at the shopfront of Sister Mai, and a little bit further is the shopfront of the Archemist. Turning left and going up the stairs leads to Brother Kane and a power armor station. Going further up the stairs will lead to the entrance to the Nucleus Command Center, guarded by a zealot.

Going straight from the Archemist's shopfront, there is a staircase that goes up on the right and a staircase that goes down on the left. The staircase on the right goes through multiple wooden shacks to end up at the entrance to the Vessel. The staircase down leads to Zealot Ware. From Zealot Ware, there is another staircase on the right that leads to the bottom of the Vessel and a ramp. The ramp also leads to the entrance to the Vessel.

Loot

 * Brother Devin's diary - Sticking out from under the mattress In Brother Devin's shack in the southwest section on the top level.
 * Footlocker key - Behind the left red bench in the storage room just before the decontamination arches. Opens a footlocker in the Vessel, available during Witch Hunt.
 * Taste test - To the right of Brother Kane.
 * Repairs in progress - Near the decontamination arches to the east.
 * Put It from Your Mind - On a chair in a shack nearest to the sub's periscope.
 * High Confessor's note - Given to the player by High Confessor Tektus during Witch Hunt.
 * Kiloton radium rifle - Sold by Brother Kane.
 * Recon Marine right and left arms - Purchased from Sister Mai / Brother Kane.
 * Atom's Judgement - Received from Grand Zealot Richter upon completion of the quest The Heretic.
 * Radical Conversion - Received from Sister Mai upon completion of the quest Ablutions.
 * Two fusion cores on the metal shelves in the first wooden shack upon entering.
 * Two cannonballs in a bucket up in the catwalks at the end of the first hallway to the west after exiting the end of the Nucleus Command Center, next to a huge pile of cans.
 * High Confessor's robes and helmet - Worn by Tektus.
 * Inquisitor's cowl - Reward from Tektus for completing the quest Witch Hunt.
 * Atom's Bulwark - Reward for completing Reformation or Cleansing the Land.
 * Robes of Atom's Devoted - Given by Grand Zealot Richter after completing Visions in the Fog.

Appearances
The Nucleus appears only in the Fallout 4 add-on Far Harbor.