Answer: Colossus

Colossus was the first computer in the world to be completely electronic, digital, and programmable. Designed by Tommy Flowers in the early 1940s and put into use in 1943, the machine was a special purpose computer focused on cracking Nazi encryption. Colossus didn’t actually directly crack the codes, but instead processed encrypted messages, simulated mechanical code breakers, and then generated potential key combinations that could be used to decipher the encrypted communication.

By modern standards, it was quite limited as far as programmable machines go. It was not possible to store programs in the machine, so each new program had to be manually entered using a series of switches and plugs. Furthermore, once the war was over, it was of limited utility since it had been designed specifically for cryptographic tasks and could not be easily retooled to serve civilian needs—but since the program was classified until the 1970s, this was hardly a concern at the time.

After the war ended, the machines (except for Colossi 11 and 12, which were dismantled in 1959 and 1960), all the documentation, and the blueprints were ordered destroyed to help maintain the secrecy of the project, and for decades, the people who worked on the project were never given credit for their accomplishments.

In the 2000s, a project to recreate a Colossus Mark 2 began using input and guidance from the remaining engineers that worked on the original computers along with some newly discovered engineers’ notebooks that had escaped destruction. The project was completed in 2007 and the rebuilt Colossus competed in a Cipher Challenge—a competition to see which code breakers around the world could decipher original WWII encrypted messages the fastest. The machine didn’t win (it lost to a modern computer), but in the process, it was discovered that the simple-purpose Colossus worked at about the equivalent of a 5.8 Mhz chip—an extremely impressive showing for a computer built in the early 1940s.