Ghost Fleet

The "Ghost Fleet" was a hypothetical Chinese stealth submarine program, speculated by parts of the DIA to be in operation as of 2075.

Background
In November of 2075, DIA stations A-31 and B-19 reported an oceanic anomaly they nicknamed the "Ghost Fleet", believing it to be linked to Chinese military submarines. A month later, an analysis of Chinese stealth technology and research capabilities by the DIA's experimental Predictive Analytic Machine concluded that there was a 91% chance that China had conducted large-scale experiments with stealth technology, and further postulated that these tests could have been conducted with submersible vessels. However, when asked to refine the answer and directly establish whether stealth submarines were in service with the Chinese navy, P.A.M. stated that the quality of the available data was too poor to arrive at any such conclusion. When pressed to offer a guess by a general, it shut down in apparent protest.

P.A.M.'s first order approximation - that the Chinese had begun macro scale research into stealth technology - was corroborated by an increase in the imports of complex polymers and other key synthetic compounds to Shaanxi Province that previously flew under DIA's radar for over three years. However, higher ups in the DIA found the secondary hypothesis of an undetected fleet of stealth submarines incredibly dubious; the general present for the initial analysis dismissed the idea of stealth subs as "nonsense", reasoning that US intelligence agents would have noticed if such a major breakthrough had occurred. The matter was buried shortly afterwards, with DIA personnel instructed not to mention the "ridiculous" idea again unless they have concrete evidence of the fleet’s existence.

Appearances
The Ghost Fleet is mentioned in Fallout 4.