GR translation: hammerfall and doomcrack

[Mike Jing]

P26.1-7   It’s nothing he can see or lay hands on—sudden gases, a
violence upon the air and no trace afterward . . . a Word, spoken with
no warning into your ear, and then silence forever. Beyond its
invisibility, beyond hammerfall and doomcrack, here is its real
horror, mocking, promising him death with German and precise
confidence, laughing down all of Tantivy’s quiet decencies . . . no,
no bullet with fins, Ace . . . not the Word, the one Word that rips
apart the day. . . .

What is "hammerfall and doomcrack" referring to here?