i had the opportunity to visit bletchley about sixteen years ago... one interesting detail was that all the colossus machines were destroyed after the war as they were seen as too powerful and dangerous. it wasn't until years later that the retired telephony engineers (this was where ee excellence lived at the time) who had built them began rebuilding them from memory as a sort of hobby/club centered at bletchley. there used to be a fellow there named tony sale who would tell you all about it, but unfortunately he passed away a few years ago.

super interesting place and worth the short trip out of london! also i believe the term they used was "semi-programmable digital computer." bombes were mechanical search machines that i believe operated on short ciphertext sequences and i believe the big innovation with the colossus was having the ciphertext live on a long optical tape that would be re-read at thousands of characters per second, thus enabling a high speed processing loop of longer sequences. but i am no expert on this!