The soviets did something of almost the same level of sanity, they used rockets to dig holes rapidly.[0] An underground rocket is basically a specialized rocke

The soviets did something of almost the same level of sanity, they used rockets to dig holes rapidly.[0] An underground rocket is basically a specialized rocket nozzle pointed straight at the ground, the hot fast moving exhaust gases are able to excavate soil and rock. Speed up to 100 m/s through soil and 5 m/s through solid rock have been claimed. Here's a video of a missile being repurposed to do this[1]. I've read, although I forget where, that there were concerns the soviets could use this technique to quickly place a nuclear weapon under west germany as part of a nuclear first strike. I suspect these concerns were quite short lived [0]https://en.wikipedia.org/wiki/Underground_rocket https://en.wikipedia.org/wiki/Underground_rocket [1]https://www.youtube.com/watch?v=e7_tRmSIIEo https://www.youtube.com/watch?v=e7_tRmSIIEo