Each COLOSSI used 1,600 vacuum tubes (Mark I) or 2,400 vacuum tubes (Mark II). The wartime codebreaking at BP was kept secret until the 1970s.

Also during the war, electro-mechanical binary computers were being developed by Konrad Zuse. The German military establishment during the war did not prioritize computer development. An experimental electronic computer circuit with around 100 tubes was developed in 1942, but destroyed in an air raid.

In the United States, work started on the ENIAC

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