a nice video on the real thing by the inimitable Professor Brailsford.

https://www.youtube.com/watch?v=9HH-asvLAj4

And a longer, deeper dive (also very good).

https://www.youtube.com/watch?v=g2tMcMQqSbA

The Colossus Machine was a huge code-breaking computer built in the UK during World War 2. Multiple models were built but most were destroyed by the intelligence services at the end of the war. So far as I understand, it calculated possible keys being used on encrypted radio messages broadcast by the Nazis.

This is a 3D model I stumbled upon that shows how it works in intricate detail.

The whole story behind Colossus is fascinating. There is a replica in the National Museum of Computing in Bletchley Park.

I bet you were told that the code brakers at Bletchley Park only decrypted "Enigma" during WWII. That is actually an old story, and is not entirely correct.

It turns out the Germans also had a much more advanced cypher called Lorenz, which required rather more advanced hardware, including the world's first programmable electronic computer. This was Colossus.