The Boring Company started with Godot, a traditional boring machine that pretty much functions like a regular TBM. Godot is believed to be the boring machine that created the Hawthorne test tunnel, and while it works just as well as a TBM could, it is also immensely slow. Following Godot, the Boring Company designed Line-Storm, a TBM that is essentially a heavily modified conventional boring machine. In terms of speed, Line-Storm is capable of at least digging twice as fast as a traditional TBM like Godot.

But Godot and Line-Storm are just the beginning. During The Boring Company’s information session, Elon Musk and Steve Davis talked about a third tunneling machine. This machine, called Prufrock, is entirely designed by the startup, and it is expected to dig about 10-15 times faster than traditional boring machines like Godot. That’s a notable improvement over conventional diggers, and it has the potential to revolutionize tunneling technology in one fell swoop.

Science fiction writers from the 1920s-1930s Golden Age loved the idea of machines that moved through the earth like submarines move through the water. It's an uncharted frontier down there!

I'm sure you'll enjoy this illustration from Ed Earl Repp's 1929 Science Wonders Stories yarn The Metal World:

In his marvelous 1936 story Death Dives Deep, Paul Ernst describes a metal earthworm:

Inside, a great arc light shed white beams over scientific paraphernalia, machine shop equipment — and the thing these elaborate devices had produced. That was a great metal cylinder, perhaps , ten feet through and twenty-five long, set up on end in the center of the dome building... "... What is this thing? Well, it's an atom compacter. In plainer language, it digs holes..."

"With it, if you liked, you could find many times its weight in gold. For with it you could sink shafts in a few hours to the deepest of metal deposits. Or you could build commercial tunnels at a rate of many miles a day. Or it could be used as a war Instrument: You could sink in it behind your own lines, burrow forward through solid earth till you were under the enemy capital, and there lay mines to be exploded when you were far on your way home again."

"It sounds to me as though you had invented a kind of metal earthworm," sniffed Ria...
(Read more about the atom compactor - a metal earthworm)