If interested, this provides more context on the Pentagon project: https://www.popularmechanics.com/military/weapons/a32700671/...
“unlike traditional tunnel boring machines (TBM), Prufrock is custom designed by The Boring Company, and it is expected to be capable of digging far quicker than its conventional counterparts.”
https://www.teslarati.com/elon-musk-boring-company-prufrock-...
Even their website is scarce of info.