The Nucleus (also known as Mount Desert Island Naval Base) is a pre-War nuclear submarine base that the Children of Atom have converted into a town and center of worship.
The Nucleus, or rather, Mount Desert Island Naval Base, is a former United States Navy submarine pen still housing the derelict USS Democracy in dry dock. Following a catastrophic leak of the submarine reactor, the base was evacuated on the eve of the Great War, with the irradiation ensuring that nobody would enter it and salvage the sub. This did not deter DiMA or Faraday, who used the base as their headquarters and living space. That is, until DiMA decided to show a little of his synthetic heart and give the base to the Children of Atom, freshly banished from Far Harbor. They seized the opportunity and under High Confessor Martin built it into a respectable center of living. That is, until Martin "disappeared" and was replaced by High Confessor Tektus, a war-mongering religious fanatic. War became inevitable.
The interior of the Nucleus cannot be accessed without violence or completing Visions in the Fog. It consists of the massive, rusted doors of the pen and a small bunker entrance leading inside. Zealots circle the perimeter, repulsing anyone interested in attacking the base.
The interior is a lot more interesting, dominated by the hulk of the Democracy. On the far end of the pen, the Children erected a shanty town where they live, work, and worship Atom. It offers the standard settlement services. High above is the entrance to the command center, which can be freely accessed.
The USS Democracy, still moored in dry dock, is now a seat of power and worship for the children. The command area has been converted to a throne room, where High Confessor Tektus sits, and behind it is the crew quarters. This area holds living quarters for the children, as well a crypt around the submarine's reactor where the deceased can be close to Atom's glow even in death. Sister Aubert takes care of the vessel, responsible for maintaining it and its reactor.
The command center is essentially a linear dungeon crawl. The path to the right of the entrance before the lasers, leads to a small storage area with a weapon workbench. The hallway in front begins the gauntlet towards the command center, filled with laser tripwires, then turrets, then a Mr Gutsy in the small barracks area, Protectrons near the mess hall, and finally an Assaultron and some more gun turrets near the command center. Once there, you can freely access the VR interface to retrieve DiMA's memories.
The Nucleus appears only in the Fallout 4 add-on Far Harbor.
- ↑ Far Harbor loading screen hints: "The Nucleus is home to the Children of Atom. It is built out of a prewar nuclear submarine base that the Children have converted into a town and center of worship."