The military has huge advantages doing this. First it will mine in seriously competent rock. This makes the mining relatively safe. Thus crews who are already experienced miners will not complain too much.
Presuming a twenty foot advance per day using blasting methods, we can have one crew or mining front produce a good mile of tunnel per year. Opening up caverns will be even faster and easier. All this produces several truck loads of waste every day which has to be dealt with. much of that would slide easily into the building trades. It is still hard to keep quiet, but then it is also not impossible.
What this shows us is that a mere one hundred mining teams could produce seventy years times one hundred teams times one mile to give us 7000 miles of working tunnels. This represents several thousand men at most continuously engaged. These numbers are easily lost inside the military.
It is clear that we have only seen the tip of the iceberg. Presume the Russians did as much as did just about every NATO power as well. Add in the rest once everyone understands just how easy it all is and what excellent training for manpower it happens to be.
In 1987 Deputy Director of Engineering and Construction for the U.S. Army Corps of Engineers, Lloyd A. Duscha, gave a speech at an engineering conference entitled “Underground Facilities for Defense – Experience and Lessons.” In the first paragraph of his speech he states the following:
Photo of United States Air Force tunnel boring machine at Little Skull Mountain, Nevada, USA, December 1982. There are many rumors of secret military tunnels in the United States. If the rumors are true, machines such as the one shown here are used to make the tunnels. (Source: U.S. Department of Energy.)
Deep Underground Command Center (DUCC)
The very first TOP SECRET memo on the subject was issued by Robert McNamara, on November 7th 1963 from the office of the Secretary of Defense. This took place right before the Kennedy murder (4).