The Bletchley Park Codebreakers (27 page)

Hut 8 then broke Seahorse (whose German codename was Bertok, derived from ‘Ber[lin]-Tok[io]’) in September 1943, again at the request of OP-20-GM, following an extensive examination of the traffic. Seahorse was employed for communications with the German naval attaché in Tokyo, Vice-Admiral Paul Wenneker, and was called ‘
Kriegsmarine
’ by OP-20-GM. It, too, used a throw-on indicator system, and turned out to be an M4 cipher.

The final throw-on system attacked by Hut 8 was Bonito (German codename,
Eichendorff
), which was first broken, ‘[a]fter a certain amount of trouble’, in May 1944. Bonito provided intelligence on midget submarines and saboteurs. The traffic increased from five to ten messages daily in April 1944 to 100 a day in spring 1945.

The use of doubly enciphered message keys was a catastrophic blunder by the
Kriegsmarine
. Such a basic security error is almost incomprehensible, especially since the
Heer
and the
Luftwaffe
had abandoned double-encipherment on 1 May 1940 because they had become aware that it made Enigma very vulnerable. The
Kriegsmarine
was definitely fully informed about that decision, but still adopted a completely flawed system. In consequence, Hut 8 and OP-20-GM penetrated no fewer than six ciphers, some of which they probably could not otherwise have broken, since no cribs were available for them.
Süd
and its subsets alone ultimately yielded over 115,000 decrypts, containing a considerable amount of intelligence about the areas they covered.

The traffic handled by Hut 8 increased considerably as the war went on. On average about 460 intercepts were dealt with each day in 1941 and 1942, 980 in 1943, 1,560 in 1944 and 1,790 in 1945. The principal naval intercept station, Scarborough, had about sixty-five receivers on German naval traffic in April 1942, most of them taking naval Enigma. There were also a number of sets abroad on naval work, including some in the Commonwealth, and a small station in Murmansk, in northern Russia. Traffic often had to be double
banked, since bombe menus depended upon accurate message texts, preferably with no omissions; sometimes Hut 8 even requested treble or quadruple banking, particularly for keys in the Mediterranean, where intercept conditions were very poor. Hut 8 did not control the intercept sets, unlike Hut 6. Instead, it requested special coverage through Hut 4, but the different system worked well in practice.

In addition to being a significant source of intelligence, shore high-frequency direction-finding (HF-DF) was Hut 8’s vital ally, especially when using the weather and sighting short signals as cribs. Moreover, without shore HF-DF it is highly probable that Banburismus would have been impossible. The only weak point in the K book indicating system was its use of a single
Grundstellung
each day in any one cipher. The
Kriegsmarine
could easily have provided for different
Grundstellungen
, but doing so early in the war would probably have increased the length of signals, making them more vulnerable to shore HF-DF. There can be little doubt that the
Kriegsmarine’s
fear of shore HF-DF strongly influenced its decision to adopt a common
Grundstellung
procedure. Shore HF-DF therefore indirectly advanced the production of operational intelligence from Dolphin by about one year, since only Banburismus enabled Hut 8 to overcome the shortage of bombes for naval work before mid-1943. By September 1942, seventeen naval HF-DF stations had been established in the United Kingdom. By May 1943, there were about twenty-three British and Commonwealth stations on the Atlantic seaboard. The US Navy also had a substantial number of Atlantic stations.

Other forms of Sigint, such as Tina (the identification of radio operators from the characteristics of their morse-sending) and radio finger-printing (RFP), which used cathode ray screens to identify individual radio transmitters, were of less assistance to Hut 8. So far as U-boats were concerned, RFP could seldom do more than distinguish between the transmitters used by the large Type XB and Type XIV boats, and those in the general mass of U-boats. Due to the high standard of German transmitters, RFP could not identify the transmitters of specific boats, which in 1944 led Naval Section to conclude that all attempts to do so should be abandoned as an aid to the production of Ultra from Enigma, although not for the purposes of general intelligence. Curiously, OP-20-G took the opposite view so far as using RFP and Tina combined to produce cribs for Shark was concerned, even though US Navy RFP gave worse results than in
Britain. Intelligence derived by Hut 4 from traffic analysis – the study of the external characteristics of signals, such as their indicators (for example, ‘w w’ for weather short signals), the volume of traffic, the radio frequencies used and so on – also helped Hut 8 on occasion.

Hut 8 in the long run gained much from its eventual close co-operation with OP-20-G but the relationship took some time to come to fruition. Mrs Agnes Driscoll, a celebrated US Navy codebreaker, and a small section in OP-20-G had begun an attack on Dolphin in November 1940, but did not have the slightest success. Following various disputes with GC&CS during the course of 1942 over the role to be taken by OP-20-G in attacking Shark, Commander Joseph Wenger, the head of OP-20-G, became exasperated by GC&CS’s failure to build four-rotor bombes. On Wenger’s recommendation, Vice-Admiral Frederic J. Horne, the US Navy Vice Chief of Naval Operations, therefore decided on 4 September 1942 that OP-20-G should embark on an extensive bombe programme, tentatively costed at $2,000,000 (the eventual cost was $6,000,000, about $48,000 (£12,000) per bombe). By 17 September, Joseph Desch, of the National Cash Register Company in Dayton, Ohio, had completed a twelve-page report setting out an outline design of a four-rotor bombe for the US Navy.

In October 1942 Travis and Captain Carl F. Holden, the US Navy’s Director of Communications, concluded the wide-ranging ‘Holden Agreement’ (sometimes referred to as the Travis–Wenger Agreement) on naval Sigint. Under the Agreement, work against Shark became the subject of ‘full collaboration’ between GC&CS and OP-20-G. GC&CS was to help the US Navy to develop ‘analytical machinery’ (the bombes) and there was to be a complete exchange of technical information on
Kriegsmarine
ciphers. The Agreement was the first to establish the vital Sigint relationship between the two countries during the war.

The British official history errs in claiming that ‘in September [1942] the Navy Department announced that it had developed a more advanced machine [i.e. a bombe] of its own, [and] would have built 360 copies of it by the end of the year’, and that the Agreement included a ‘compromise’ under which the ‘Navy Department… undertook to construct only 100 Bombes’. No US Navy bombe of any kind had been developed by September 1942. Neither the original US Navy directive for the bombe project nor the Holden Agreement
specified the number of bombes to be built. OP-20-G’s decision to build only about ninety-five bombes was not taken until March 1943.

One of the first two US Navy bombe prototypes, named Adam (the other was ‘Eve’), was delivered to the Navy Computing Laboratory in Dayton on 26 May 1943 to begin tests. There were countless problems, with both machines, especially with ‘shorts’, ‘opens’ and oil leaks. Neither machine was running well as late as July 1943. However, the problems were eventually sorted out, and production models began to be shipped to Washington, DC, in late August. Some production bombes were in ‘semi-continuous operation’ by 11 August, with six operating by 7 September.

The standard US Navy bombe, known as a ‘530’, was about 2 ft wide, 8 ft long and 7 ft high and weighed 5,000 pounds. The British three-rotor bombe was a few inches smaller, but weighed only about 2,200 pounds. The Navy bombe had at least three hundred valves – quite a large number for that time. The Navy’s 530 type bombes only had sixteen banks of Enigmas – eight on each side (see page 7 of the plate section). They could therefore only run short menus, with a maximum of sixteen letters. OP-20-GM eventually built three double unit bombes, known as the 800 bombe (nicknamed ‘granddad’), which contained thirty-two banks of Enigmas, to tackle ciphers such as Seahorse. The first 800 unit became operational at the end of January 1944.

About ninety-five of the Navy 530 type bombes were made, including eight inverted machines. A 530 bombe ran a three-rotor menu in a mere fifty seconds, and a four-rotor menu in twenty minutes. However, due to the time required to set up a bombe menu and change rotors between runs, the average production per watch of eight hours was between forty-eight and sixty three-rotor runs (known as short runs) or twelve four-rotor runs. Twenty-three units of an improved model, the 1530, with circuitry which reduced the number of false ‘stops’, were also built. The US Navy also used a number of ‘black boxes’, called ‘grenades’ (being small bombes), which were attached to bombes to deal with various Enigma problems where the
Stecker
were known. The standard grenade, for example, was used to locate the rotor starting positions when the rotor order, ring settings and
Stecker
had been found.

Once the Navy bombes were moved to Washington, they worked well, and were extremely reliable. Thus in April 1944, when eighty-seven
Navy bombes were in service, their down-time was about 2.7 per cent, while routine maintenance required about 2.5 per cent. This was just as well, since the British four-rotor bombes were far from reliable. In early 1944, only twenty-five or so four-rotor bombes had been installed at GC&CS. In March, their performance was described by Hugh Alexander as ‘still poor, and likely to remain so’. Very few, perhaps only three, were actually operational then. In consequence, GC&CS decided that future British bombe production would be concentrated on making three-rotor bombes, although a further eighteen or so four-rotor bombes were in fact made.

The US Navy bombe figures for maintenance and reliability were maintained consistently throughout 1944 and 1945, each being under 3 per cent. Like some British bombes, some US Navy bombes continued to operate after the end of the war in Europe: one Navy bombe was still attacking old wartime ciphers in March 1946. It has even been claimed that some were brought out of storage to tackle an East German police version of Enigma in the early 1950s.

After Hut 8 re-entered Shark in mid-December 1942, OP-20-G broke a few keys manually. By the end of 1943, with about
seventy-five
bombes in service and considerable experience under its belt, OP-20-GM was allocated responsibility for breaking Shark. At first, OP-20-G used cribs sent by Hut 8. However, they soon started to devise their own cribs. By August 1944, Hut 8 had only four cryptanalysts (Rolf Noskwith, Joan Clarke (one of Bletchley’s very few female cryptanalysts), Patrick Mahon and Richard Pendered) – very few, bearing in mind that a three-shift system operated, and that there had been sixteen in February 1942. The number of Shark keys solved by Hut 8 gradually diminished. It solved only five Shark keys in January 1945, none in February and one in March.

The US Navy bombes very soon had spare capacity. Although the Navy was very apprehensive about trespassing on the US Army’s preserves, it agreed to run Hut 6 (Army and Air Force) problems (codenamed Bovril). However, tackling this work for Hut 6 ran counter to an allocation agreement with the Army on the division of work that had been agreed by President Roosevelt in 1942. Eventually, a somewhat reluctant Travis was pressed by Rear Admiral Joseph Redman to obtain the approval of Colonel Carter Clarke, the chief of the Army’s Special Branch, for the work being done by the Navy. Clarke agreed, but gently chided Travis and Redman for
having put the work ‘into operation without our prior knowledge’. In January 1944, about 45 per cent of the Navy’s seventy-five bombes were on Hut 6 work, while about 60 per cent of its 115 bombes were so engaged in January 1945. The number of Navy bombes on Hut 6 jobs therefore rose from roughly about thirty to seventy during 1944.

GC&CS had about seventy three-rotor bombes in service in January 1944, and 140 in January 1945. Allowing for set-up times, and changing rotors, one US Navy four-rotor bombe could do about three times the work of a GC&CS three-rotor bombe. The seventy Navy bombes on Hut 6 work in January 1945 were therefore equivalent to about 210 GC&CS three-rotor bombes, increasing GC&CS’s
three-rotor
bombe capacity by 150 per cent. This was extremely fortunate, since GC&CS needed all the bombes it could get. Indeed, in February 1944, GC&CS had asked OP-20-G to order fifty additional bombes. They were duly requisitioned, and started to enter service in mid-August. However, the existing US Navy bombes were found to be so efficient that the additional order was reduced to twenty-five in September.

From June 1943 to June 1944, OP-20-GM recovered:

The
Kriegsmarine
began to issue special Enigma ciphers (
Sonderschlüssel
) to individual U-boats in mid-1944, but did not use them until mid-November.
Sonderschlüssel
were virtually unbreakable, since very few cribs were available: it took 5,300 bombe hours and about six weeks’ work before
Sonderschlüssel
161 succumbed in early April 1945, and only three
Sonderschlüssel
were ever broken, all by OP-20-G. The widespread use of
Sonderschlüssel
from February 1945 onwards deprived the Allies of virtually all operational intelligence on the U-boats. However, even worse was to come. On 1 April 1945 Plaice, a cipher used in the Baltic, implemented ‘one of the most formidable changes’ made by the
Kriegsmarine
, by employing a set of 288
Grundstellungen
for April, instead of a single daily
Grund
. Hut 8 had to break a considerable number of individual messages in
order to reconstruct the list of
Grundstellungen
, and could do so only because a new machine, Filibuster, was available. Hut 8’s problems were compounded when Dolphin adopted the new system on 1 May – and a fresh set of 288
Grundstellungen
took effect for Plaice. Hugh Alexander was by no means certain that Hut 8 could have survived these changes. At least twenty-four more examples of Filibuster and another machine (Hypo) would have been required, as well as a greatly increased staff. Even then, the outlook would have been uncertain.