FT MAGAZINE 
“Colossus arrives today,” wrote Max Newman, one of the mathematicians working on breaking German codes at Bletchley Park, in a memo dated January 1944.
Colossus was a top-secret, room-sized computing machine that was not only to provide crucial information in the run-up to the Allied invasion of Europe but would also be a landmark in the evolution of computers.
In 1943, the cryptanalysts at Bletchley Park, famous for cracking the German Enigma code, had turned their attention to the even more complicated coded messages sent between Hitler and his generals, which were mechanically encyphered using a so-called Geheimschreiber, a teletype-based machine that turned each character of a message into a set of five binary digits.
The creator of Colossus was Tommy Flowers, a working-class telephone engineer based at a Post Office research station in Dollis Hill, north-west London. In 1943, after seeing the unreliable “Heath Robinson” machines being used at Bletchley Park, he decided to come up with his own design based on 1,500 of the electronic valves, or vacuum tubes, used in the British telephone system.
The codebreakers were sceptical about the reliability of a machine with so many valves, but after working round the clock for 10 months and even investing some of his own money in the project, Flowers demonstrated the prototype. It functioned perfectly. It was taken apart and brought up to Bletchley Park, where it later provided vital information about German troop movements in advance of the D-Day landings.
Colossus was the first large-scale electronic computing machine. It did not have an internal memory and therefore had to be reprogrammed for each run. But in employing the binary logic that made it possible to do large calculations electronically, it was revolutionary.
After the war was over, Newman and Alan Turing helped develop the next stage in fully programmable computers, based on the advances made at Dollis Hill and Bletchley Park. But the Colossus project itself would remain a secret for decades and Flowers would remain largely unknown until his death in 1998.
