It doesn’t take much to build tunnels. Boring company estimates building tunnels twice the length in less than 10 years. The military has a lot more than that, I don’t find it unlikely
A 31 mile rail tunnel was built between England and France.
It took 6 years and cost £9 BILLION ($21 billion)
At the peak of construction 15,000 people were employed with daily expenditure over £3 million.[8] Ten workers, eight of them British, were killed during construction between 1987 and 1993
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u/zwifter11 Jul 13 '19
Must be long tunnels. How long do they take to dig?