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.
The biggest difference between enigma and Lorenz was Lorenz was broken without seeing a physical machine. It was broken as a very long message was transmitted twice with minor changes. That allowed recovery of of the plaintext and key stream
https://www.youtube.com/watch?v=9HH-asvLAj4
And a longer, deeper dive (also very good).
https://www.youtube.com/watch?v=g2tMcMQqSbA