They may have been though - there's talk of liquid helium tens+ of gigahertz (8-bit) processors being purpose built (in 2002). The National Cryptologic Museum next door to NSA HQ is a fascinating place and has some very cool displays to include a large disk changer and a piece of a cooling system. There's a PDF at [1] but the discussion at [2] I think might give a better idea.

[1]: https://www.nitrd.gov/pubs/nsa/sta.pdf [2]: https://it.slashdot.org/comments.pl?sid=485458&cid=22736288