A Lorenz SZ42 cipher machine. The front cover is open to reveal 12 cipher wheels, each of which contains between 23 and 61 settable pins. The wheels worked together in two sets, one set rotating all the time, the other moving intermittently. The wheel settings and rotations worked together to create a complex cipher.
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75 years since Colossus arrived at Bletchley
On 18 January 1944, the first Colossus machine arrived at Bletchley Park. Just as Bombe machines had been developed to help Bletchley Park’s Codebreakers decipher Enigma messages, Colossus had been commissioned to help break another, even more complex German machine cipher: Lorenz. To tackle Lorenz, Bletchley Park needed Colossus to be capable of statistical analysis, not just to cycle through all possible cipher settings one at a time. A team of General Post Office engineers, led by Tommy Flowers, rose to the challenge. They designed an ingenious system that used electronic valves to store information, making Colossus the world’s first large-scale electronic digital computer.
This Collections Uncovered album was first published on 18 January 2019.
Colossus machine No. 7 installed in Block H at Bletchley Park, in around April 1945. The high-speed printer on the stand in the middle of the photograph was used to print out possible Lorenz message decryption settings. It had a carriage return motion so fierce that it made the stand shuffle across the floor until it unplugged itself from the Colossus. Ropes used to lash the printer to the stand and the stand to the Colossus frame were removed for this official photograph.
This view of Colossus No. 7 shows the electronics attached to two frames with an access walkway between them. The four large boxes on the right are the power supply units.
Colossus machine No. 10 in Block H at Bletchley Park, in around April 1945. Note that the various panels and the two tape machines are arranged in the reverse order to those of Colossus 7, indicating that the machines were not all put together in the same way.
The rear view of one of Colossus No. 5’s electronics frames. Row upon row of valves can be seen either side of the of the white central section which is itself marked to indicate which panel is working on which Lorenz wheel.
Colossus machines were operated by Wrens – members of the Women’s Royal Naval Service. Here Elsie Booker (right) is adjusting one of the tape machines while Dorothy du Boisson looks on.
Around 250 Wrens kept Bletchley Park’s 10 Colossus machines running 24 hours a day. Peggy Diana Clarke was an experienced operator who had also run Colossus’ predecessors, known as Robinson machines.
After the war Bletchley Park’s Colossus machines were dismantled and the components dispersed. This focal lens was rescued from a pile of scrap equipment being thrown away in 1970 and was donated to Bletchley Park Trust more than 40 years later
Some parts from the dismantled Colossus machines were later reused by the Computing Machine Laboratory at Manchester University. This facility built the Manchester ‘Baby’, the world’s first working general-purpose stored-program electronic computer. Baby was later developed into the Ferranti Mark I, the world’s first commercially produced computer. The valve shown here is on display at Bletchley Park.
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