Yangtze

The Yangtze or Yangtze-31 is a Liao-Class Type 113 Chinese nuclear-powered ballistic missile submarine commanded by Captain Zao. When first discovered by the Sole Survivor, it is lodged in the shallow waters of Boston Harbor south of Boston Airport and northeast of the Four Leaf fishpacking plant.

Background
Sometime before the Great War, the Yangtze was on deployment with a payload of six warheads, all but one launched. Shortly after firing, the submarine struck a mine that severely damaged the reactor and forced the vessel to seek shelter in Boston Harbor. The damage caused a reactor leak that immobilized the sub and ultimately killed or ghoulified the crew, of which only Zao retained his sanity.

The submarine is not marked on the map until the Sole Survivor swims out to it. Upon discovery, the quest Here There Be Monsters will automatically be started if it hasn't been received already from Donny Kowalski near the Shamrock Taphouse.

Layout
The Yangtze has three large propellers, with one on each side and a third under the reactor control room, as well as a smaller propeller at the rear of the submarine with the rudder. Upon entering the ship, the first room the Sole Survivor comes to is the bridge where Zao is located. Down the stairs is the reactor control room, with a small radio room on the left side ahead.

North of the reactor room on the upper level is a small room that contains two decontamination showers and an Expert terminal-locked door with a stairway to the lower level. There is also a small science lab with a chemistry station. North of the crew quarters are two doorways that lead to a single stairway down into a room with a workshop containing a weapons workbench. The next room to the south is a small room before the reactor room, containing a terminal-locked door to the stairway to the upper level.

Loot

 * Submariner uniform and submariner hat - Worn by Captain Zao.
 * Zao's sword - Possible reward for completing the quest. Only obtainable if all Speech checks are passed when first requesting a larger reward near the start of the quest.
 * Chinese officer sword - In the captain's quarters, on a desk.
 * Two fusion cores - One is in a box underwater on the east side of the lowest level of the engine room, just past a skeleton lying on a barrel. The other is inside an open footlocker in the crew quarters, near the Nuka-Cola Quantum.
 * Vault-Tec lunchbox - In the galley, on the table in the southeast corner.
 * Nuka-Cola Quantum - In the crew quarters, next to the bunk of the dead crew member holding a Nuka-Cola truck.
 * Stealth Boy - In the armory, inside the Master terminal-locked cage.
 * Submariner hat - In the silo room, worn by the first mate, now a glowing one.
 * First mate's password - In the silo room, on the first mate.
 * Warhead - In the silo room, in the capsule on the west wall.
 * Hazmat suit - In the silo room, in a locker to the southeast. The door to the locker must first be manually opened to reveal the suit and other minor loot.

Related quests

 * Here There Be Monsters: Living on the ocean shorefront is a boy named Donny Kowalski, who asks the Sole Survivor to help him determine what he has been seeing out in the water recently.

Companion comments

 * When at this location, companions make comments, which are activated at three locations: the bridge, the engine room, and after placing the warhead in the reactor.

Appearances
The Yangtze appears only in Fallout 4.

Behind the scenes
Josh Jay posted an Artstation showcase of the submarine, identifying it as "The Chinese stealth submarine in Boston Harbor that launched nuclear missiles against the mainland in Fallout 4." The showcase also includes a logo of the Chinese People's Liberation Army Navy.