Tutte and Flowers – Bletchley Park’s Lost Heroes


It all started with the German Lorenz machine – Hitler’s state of the art encrpyting communications machine – Enigma had been broken in 1941, but this time his new machine was almost un-decypherable

The Lorenz SZ40, SZ42a and SZ42b were German rotor stream cipher machines used by the German Army during World War – they were known as the “Tunny machine” to British intelligence codebreakers and whereas a lot is known about  Germany’s “Enigma” code-encrypting machine which required 3 people to send and receive the code – the “Tunny” was more automated and had a lot more encrypting permutations   – in fact it encrypted a letter twice over and more –  the number of enciphering possibilities work a out as :

23 x 26 x 29 x 31 x 37 x 41 x 43 x 47 x 51 x 53 x 59 x 61 = 1,600,000,000,000,000 or 1.6 million billion combinations.

British cryptanalysts, who referred to encrypted German teleprinter traffic as ‘Fish’, dubbed the machine and its traffic “Tunny” (short for Tuna Fish)

The SZ machines were in-line attachments to standard teleprinters. Radioteletype (RTTY) rather than land-line circuits was used for this traffic. These machines no longer used Morse code to deliver messages and a message was picked up by Britain’s Y-stations at Knockholt and Denmark Hill and sent to Government Code and Cypher School at Bletchley Park. Some were deciphered using hand methods before the process was partially automated, first with Robinson machines and then with the Colossus computers.The deciphered Lorenz messages made one of the most significant contributions to British Ultra military intelligence and to Allied victory in Europe.

Thomas Harold Flowers (who died in 1993) was an English engineer with the British General Post Office (Ed Note: He worked at what was the GPO building in Dollis Hil, later to become a BT telecommunications research statio and was the place where they built the speaking clock; I passed it daily on my way home). During World War II, Flowers designed and built Colossus, the world’s first programmable electronic computer, to help solve encrypted German messages.

Up until the start of the war codebreakers had been using machines like the Bombe (famously only worked on  by Alan Turing in the film “The Imitation Game” when in reality there were many more people involved in it’s making and design).

However Flowers proposed a more sophisticated alternative, using an electronic system, which his staff called Colossus, using perhaps 1,800 thermionic valves (vacuum tubes) instead of 150 and having only one paper tape instead of two by generating the wheel patterns electronically. Because the most complicated previous electronic device had used about 150 valves, some were sceptical that the system would be reliable

The mathematician behind the encrypting and decyphering of the Lorenz code which in turn make the mathematical concepts for the Mark 1 Colossus was William Tutte (died in May 2002) a British-born Canadian codebreaker and mathematician. During the Second World War, he made a brilliant and fundamental advance in the cryptanalysis of the Lorenz cipher. The high-level, strategic nature of the intelligence obtained from Tutte’s crucial breakthrough, was in the bulk decrypting of Lorenz-enciphered messages specifically, even decisively, to the defeat of Nazi Germany.

Below is William Tutte and Tommy Flowers’ story in BBC’s Timewatch “Codebreakers : Bletchley’s Lost Codebreakers”

Click or Tap on image above to view “BBC’s Timewatch Series “Codebreakers: Bletchley’s Lost Heroes

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