This historical background is an edited version of a Bletchley Park top secret end-of-war report on the Bombe, National Archives reference HW3/146 – Squadron Leader Jones’ Section.

When World War Two ended in Europe, the number of people involved with the Bombe project was 263 men – mostly RAF – and 1,676 women – all WRNS. In all, there were 211 machines.  But the project had begun in 1940 in a modest way, with just three people, representing the three Armed Services.  The first Bombe came into operation at Bletchley Park on 14 March 1940 when the unit was working in half of Hut 1, the other half comprising the sick bay! The entire Bombe unit was crammed into an area 15 feet by 12 feet, which was, on occasion, also the dining room and sleeping quarters.

Besides this first machine – optimistically dubbed ‘Victory’ – there was also a ‘baby’ known as ‘The Test Plate’ but with the arrival of Victory, this machine took second place.

Victory was only out of action 42 hours in the first 14 months, during which time extra innovations and modifications were added. At first all the work of Victory was for the naval codebreaking section in Hut 8, and an improved version, Machine No 2, known as ‘Agnus’ or ‘Agnes’ – affectionately known as ‘Aggie’ – came on stream on 8 August 1940.

It was the first machine to be fitted with the diagonal board, which greatly improved the Bombe’s efficiency (discussed later). In those days the time between receipt of a machine from the works at the British Tabulating Machine Company (BTM) at Letchworth in Hertfordshire led by Harold ‘Doc’ Keen (discussed later) to the start of the first run was three or four hours, during which time the machine had to be fully installed, checked for shorts, open circuits etc., and then plugged up.

During 1940, the two machines assisted in breaking 78 jobs, with only two jobs missed, an efficiency rate in the first year of 98.8%.

In 1941 it was decided to increase the number of Bombes and to employ Wrens as operators, leaving the men to look after the machines. For security reasons it was decided to send machines to out-stations, the first being at Wavendon, where Victory was sent after being fitted with the diagonal board. By the end of March 1941, another machine had been delivered which was the first to be fitted with an automatic typewriter to print and check stops, known as a ‘Jumbo’. Later 3 Wheel typewriter machines were all known as Jumbo-type.

Eight Wrens arrived on 24 March 1941 and with an increase in staff and Bombes, another outstation, at Adstock, was opened that month. At the same time the Section moved from Hut 1 to Hut 11. During the life of the Section, nearly 3,000 Wrens were trained. The requested establishment later on was for 1,850 Wrens and 275 men to operate and maintain 202 machines. By the end of 1941, there were 16 machines in operation, six in Hut 11 and five each at Adstock and Wavendon. The record was now 1,344 jobs done, 844 ‘jobs up’ and 39 missed – an efficiency rate of 95.6%.

The Bombe Section moved to Hut 11 in March 1941

In February 1942 a new building, Hut 11a, was completed next to Hut 11, which remained for office purposes but was later given up to another administration section. That month saw the addition of two more Bombes. With the Section’s growth a room was set aside fitted with telephones to codebreaking Hut 8 (Navy) and Hut 6 (Army and Air Force), as well as to Adstock and Wavendon. By the end of March 1942, there were 26 Bombes in operation and in September a third outstation was opened at Gayhurst. The same month Victory was removed from operational work but was kept for experimental and instructional purposes to the end of the war.

On 6 November 1942 a new type of Bombe arrived, a nine-chain special machine for Peter Twinn’s section, which handled German Secret Service (Abwehr) Enigma-enciphered messages, in Hut 16. It was installed in Hut 11a and ran a completely different type of menu from the other machines and was known as ‘Funf’ after a popular radio mystery character of the time. Fünf is German for five. By the end of 1942 the expansion of the Section was such that a major new outstation was built at Stanmore in Middlesex, consisting of 10 large bays, each as big as Hut 11a, and was operational by November. At the end of 1942, there were 49 Bombes operational. The number of jobs completed was 5,772, jobs up were 3,685 and jobs missed were 148 – an efficiency rate of 96%.  Staff comprised 571 Wrens, 49 RAF, three RN and seven civilians and War Reserve.

By early 1943, the mechanical times for Bombes to complete a run was 16 minutes.  March 1943 saw the first of the high-speed Keen-type machines, named after ‘Doc’ Keen, and was delivered to Stanmore. This had four sets of wheels, and the ultra-fast wheels turned 26 times to every single revolution of the normal fast position, and a three-wheel run could be completed in one and a half minutes. The first of these machines – No.101 – remained at Letchworth, and No. 102 (called Darwin) was the first of its type to become operational.

There was another type of high-speed four-wheel machine, which had been in use since August 1942, devised by Dr Charles Wynne-Williams of the Telecommunications Research Establishment, run and maintained by GPO engineers, but was more experimental than operational. In March 1943, the first Bombe of this type was delivered to Stanmore. This was an ordinary three-wheel Bombe with a high-speed fourth wheel attachment known as the ‘Cobra’, installed in two specially fitted bays at a new outstation at Eastcote, with 12 bays, which commenced in September 1943, although it was not officially opened until early 1944. By now the expansion of the Section led to a complete internal telephone system being installed in Hut 11a with, in addition, teleprinters being fitted to each outstation. By the end of 1943, there were 99 machines in operation, with 14,965 jobs done, 9,064 jobs up and only 282 missed – an efficiency rate of 97.6%.


An Abwehr four-wheel Enigma broken on the Funf machine


In early 1944, Hut 6 required an outstation for special work and this was carried out at Wavendon, which ceased to be part of the Section. Over time Bombes were moved around, and a special vehicle was constructed, large enough to completely house a Bombe without having to dismantle any of its parts. Inside the van was a heavy geared winch with cable and tackle, and a pair of detachable steel rails were carried to be fixed from the end of the van to the ground. One man was responsible for driving the vehicle and loading it, and he remained in this job throughout the war. Thus machines could be moved with secrecy and the minimum amount of disturbance. On 31 January 1944 the first of a new type of 3 wheel machine was installed at Eastcote, this Bombe – No. 250 – being fitted with Siemens BTM relays.

During 1944 two serious incidents took place affecting Eastcote and later Stanmore. On 19 February 1944, shortly after midnight, incendiary bombs fell on the Wren’s side of the Eastcote building, and there were unexploded incendiaries on the ground and a large container had crashed through into one of the work bays. Fortunately, there were no casualties. On 18 December 1944, a flying bomb – V1 – fell about 120 yards from the Stanmore working block at 4.30am, but due to the high-blast wall, the full effect of the explosion was not felt inside the block, where about 160 Wrens and 20 RAF were working at the time. Again, there were no casualties and damage was superficial.

In March 1944, a special American bay was set up at Eastcote comprising 10 machines, run entirely by personnel of the 6812th Signal Security Detachment, US Army. Although under the overall control of BP Head of Section, they had their own officers in charge and completely separate personal administration. During their operations, this unit solved 425 Enigma keys.

In June 1944 an experiment was conducted to couple together, electrically and mechanically, four three-wheel Bombes, known as a ‘Giant’. This was constructed and remained at the BTM factory in Letchworth and was the only machine to run a secure job outside a secure establishment. However, further discoveries and developments made it obsolete, because greater speed was necessary to produce the required results. Therefore, the same principles were applied to two High-Speed machines, known as the ‘Ogre’, but the urgency for its use arose before it had left the experimental stage at BTM, and it commenced operations there. It was never delivered to the Section, whilst Giant was separated and run as four ordinary Bombes. These machines never became part of the work of the Section.

The results for 1944 were almost as great as the whole of the previous years put together, with 15,302 jobs done, 8,444 jobs up and only 460 missed – an efficiency rate of 97.9%. By the end of 1944 there were 192 machines operational.

By 1945 it was decided that all future new Bombes would be 3 wheel types, (as the battle of the Atlantic had been largely won it was German Army and Airforce Enigma that needed tackling therefore 3 wheel machines with fast Siemens relays were produced) with a target of 72, but 12 were still to be delivered when the war ended on 8 May. On this date all the machines stopped running – the first time this had happened since commencement in 1940.

Dismantling began the next day. However, it was decided to keep a few Bombes running for research etc., and to retain 50 machines of various types, overhauled and stored away. The work of three machines for Peter Twinn’s Section continued for some time after VE Day, but they, too, eventually stopped work. The final figures of the Section were:



Old three-wheel 59
New three-wheel 68 (See above)
Jumbos 14
High-Speed Keen 54
High-Speed WW 12
Returned to Works – High-Speed Keen  (one never left the factory and was kept there as a reference machine)


Jobs done (1940-45) 36,002
Jobs Up 20,414
Jobs missed 505
Efficiency 97.6%


RAF 256
RN 2
Civilian, War Reserve 4
WRNS 1,676
TOTAL 1,939

However, work did not completely stop even with the surrender of Japan in August 1945. Eastcote was the first outstation to be completely cleared. It was decided to recommence some operational work (the nature of which is even today unknown), and 16 Bombes came back into action.

Instead of keeping Stanmore open, Eastcote was reopened and the machines all had to be moved once more, from Stanmore to Eastcote. Some were to be stored away but others were required to run new jobs and 16 machines were kept comparatively busy on menus.

Interestingly, most of the post-war jobs came up, and the operating, checking and other times maintained were faster than the best times produced during the war! During this period the staff was reduced considerably, all the Wrens left the Section and the RAF personnel was reduced to 80 to finish dismantling, operating and disposal of scrap material. The Section was finally wound up at the end of 1945.