The depth and defense of the Pig Bay underground city district are sufficiently guaranteed.
The nuclear bombs, about 200,000 tonnes in yield, carried by hovercrafts cannot breach the fortress made of ultra-high-strength concrete below one hundred meters.
The old Chinese have abundant experience in [deep digging and stockpiling food], especially in underground works against nuclear bombs, unmatched in this field. Back in the day, they almost dug through every mountain in the north.
Now with a large array of advanced engineering equipment, they are obviously doing it even more vigorously. In half a year, they have literally carved out an industrial zone underground, enough to support the lives of tens of thousands of people, covering seven or eight square kilometers, with a depth of sixty or seventy meters. Moreover, they are continuously adding numerous steel structure frames as filling, which can be entirely called a permanent underground fortification.
