Second World War

Bombe Machines

In the Second World War, BTM was approached to build the bombe machines that Alan Turing and Gordon Welchman devised to crack the Enigma code. BTM’s chief engineer, Harold Keen, turned the mathematicians’ ideas into reality, using the design ideas that he had used to develop the Rolling-total Tabulators (launched by BTM in 1935). The first bombe machine, named Victory, arrived at Bletchley Park (known at BTM as Bureau B) in March 1940.

Over the next few months various modifications were made to the prototype, most importantly Welchman’s diagonal board, which massively speeded up the process of decryption. From 1940 to 1944 BTM manufactured over 200 bombe machines, known internally as CANTAB machines, some of which were installed at Bletchley Park but many more were delivered to out-stations at Eastcote (100) and Stanmore (75) in North-West London. By the end of the war it is estimated that there were 1,676 Wrens working as bombe operators.

Each bombe required two women working an eight hour shift, three shifts a day, seven days a week. It was physically demanding and required intense concentration, nimble fingers, precision and attention to the maintenance of the machine. The women stood throughout their shift in an airless room made hot and noisy by the machines with their greased metal stink.

Replica bombe machine at Bletchley Park Museum

BTM had to divert over 70% of its production capacity to this work and its suppliers were also under government orders to prioritise the manufacture of whatever BTM required. It was an enormous logistical task trying to produce enough machines to satisfy the needs of the government. As the war went on and more and more machines were ordered, BTM had to somehow find the staff (and provide them with accommodation, transport and catering), raw materials, specialist parts and factory capacity to keep up with demand.

Tabulators at Bletchley Park

As well as the highly specialised bombe machines, BTM also supplied its ‘ordinary’ Hollerith tabulating machines to Bletchley Park to help with a variety of computational tasks. Mr Frederick Freeborn was seconded to Bletchley and headed up a department of machine operators in Hut 7. As time went on the computational needs increased and staff numbers burgeoned – or would have done if it weren’t for labour shortages. An anguished letter to the Treasury, dated 24 September 1940, reveals the frustration of the Bletchley tabulating team:

            “Tabulating machine operators may be “quite common phenomena” in other government departments but, even so, they seem to be rather elusive common phenomena – and Supervisors seem to be non-existent common phenomena.

            I wonder if a request for a few extra guns would be dealt with by the Treasury with the same speed and lack of understanding.” (MVM, 24/09/1940, TNA:HW64/29)

In the end Freeborn had a staff of over 100, doing a wide range of computations in support of the various sections at Bletchley Park. As was usual, female clerks of the same age and grade were paid less than their male counterparts. A Grade I male clerk aged 20 was paid £3. 14s. per week (plus overtime if more than 48 hours worked) compared to £2. 18s. 6d. for female clerks (plus overtime), 79% of the male rate of pay (TNA: HW64/29)

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