A Yangtze-class submarine stuck in Boston harbor, the Yantgze-31 is helmed by Captain Zao of the Chinese Navy. During the Great War, the Captain launched the six high-yield nuclear ballistic missiles against the Commonwealth, as ordered. However, when they tried to retreat, the Yangtze struck a sea mine and wound up moored in Boston Harbor, mere inches under the surface. Luckily for them, the burning Boston cared little for those who just nuked it - and so, the submarine remained stuck in the harbor, slowly deteriorating, its crew turned into ghouls and worse.
The submarine is hidden just beneath the surface of the water, among ship wreckage and flotsam. It can be identified by the periscope rising upwards to scan the skyline for hostiles.
The submarine is built around the forward nuclear reactor. The player enters through the conning tower, which connects to the bridge (with Captain Zao) and through it, to the rest of the ship. The primary deck is divided into two halves: The upper and lower decks, with the reactor smack right in front of them occupying both levels.
Beyond the reactor, the upper decks contain a small lab with a chemistry set, a large mess hall, pantry, kitchen, and living quarters for the crew, as well as a small security station and infirmary. The decks below contain the forward machine shop, launch tubes (with an exposed ICBM ripe for scavenging), the armory and storage holds and right under the reactor control room, the primary turbine.
- In the infirmary, a skeleton of an American soldier is on the bed along with handcuffs and a bone cutter.
- After using console command
tmm 1to reveal all locations on the map, Yangtze-31's location is not revealed.
Yangtze-31 appears only in Fallout 4.
- Zao: "200 years ago, I launched all of Yangtze's high-yield nuclear missiles. As ordered. For 200 years, I have lived with that guilt. That shame. So much fire Such bei. But one missile failed to launch. You must go down. Remove the warhead. Then bring it to me."
- Zao: "Wa! It has been that long? Shi de. Yes. I suppose it has. Long ago. Just after the fire. Yangtze struck a mine. My qianting barely made it here into harbor. City already ruins by then. Few noticed us. Fewer cared. Too much tong ku."
- Fallout 4 Vault Dweller's Survival Guide Collector's Edition p.507: "[17.04] YANGTZE
Easily mistaken for a strange aquatic monster, this Chinese nuclear submarine (Liao-Class Type 113) is hidden among the wrecks of other ships in the Boston Harbor. It is commanded by Captain Zao. Should you wish to access the terminal (Master) on the lower level, find the first mate’s password from the fellow lurking down in these parts."
(Fallout 4 Vault Dweller's Survival Guide Map)