The rise to prominence of the translators – their pivotal position was already an accomplished fact by the winter of 1940–41 – inaugurated a revolution which gave primacy to the end over the beginning.20
A navy, army or air expert assessed and annotated the translation to underline its significance. He would add, for instance, references to a unit, a place or person mentioned, bringing into use the big card-reference system that each service maintained. The next stage was the drafting of a signal to the field commander who could make use of the intelligence. The syntax of the message was changed, or ‘sanitized’, so that if the Germans encountered it they would not be able to identify the original message and guess how it had been obtained.
The British army monitors at Chatham, on the Thames Estuary, and later other stations too, listened to all German short-wave radio traffic. According to the weather, reflections from the upper atmosphere would sometimes enable transmissions from U-boat to U-boat in the farthest reaches of the Atlantic to be heard.
The Enigma coding machine was a remarkable invention. The most surprising aspect of the story is that the experts agree that a few simple changes to the original design could have made it fool-proof in use, and its output totally invulnerable. Messages were usually broken because of German carelessness and lax procedures. The Luftwaffe provided most opportunities; the navy was far more careful, so the German navy’s Enigma codes were not broken on anything like a regular basis. A founder member of the Bletchley Park team commented: ‘At any time during the war, enforcement of a few minor security measures could have defeated us completely.’21
In any case it wasn’t necessary to understand what a message said to benefit from knowing where your enemy was. High Frequency Direction Finding (HF/DF or what the Royal Navy called ‘Huff Duff’) could estimate the position of U-boats (or enemy surface ships) by getting a compass bearing on the transmissions. BP staff also made valuable assessments of German preparations and operations by studying the volume, character and point of origin of signals traffic.
Oscilloscope patterns (which depict voltage or current fluctuations on a cathode ray tube) were also photographed and filed to provide a ‘fingerprint’ that could positively identify a radio transmitter, and this in effect was enough to identify a ship or U-boat. Such fingerprinting was another of Lt Merlin Minshall’s ideas. It was in this way that the Bismarck was positively identified.22
Britain’s Secret Intelligence Service retained control of their GC&CS, and so deciphered material went to their Broadway HQ for distribution to whoever ‘C’ – Colonel Stewart Menzies, the organization’s chief – thought deserving. The Royal Navy did not trust SIS with this task, and right from the beginning the navy kept its facilities at Bletchley Park entirely separate from those of the army and the RAF. The admirals had not been satisfied with SIS since November 1939 when Menzies, an army man, was appointed to be ‘C’. The navy said that previous SIS chiefs – Captain Smith-Cumming and Admiral Sinclair – had established a tradition that ‘C’ would always be a job for a sailor.
So all naval material was handled independently and went to the OIC (Operational Intelligence Centre) in Whitehall. In early 1941 the OIC moved to the Citadel (a lumpy brown granite building between Admiralty Arch and Horse Guards; it is still there, mercifully hidden under ivy).
The navy’s system worked reasonably well. By the end of July 1941 – due largely to the capture of some Enigma machine rotors and dated settings in February, March and May – there was regular interception of Enigma signals. These were being added to all the other signals intelligence, collectively known as SIGINT, which included data from diplomats, foreign newspapers and secret agents, as well as from interrogating, bugging and planting stool-pigeons among captured U-boat crewmen. It was all analysed and put together, and with these sources the Admiralty’s Submarine Tracking Room tried to predict the intention of the U-boat captains.
Radio transmissions from U-boats were few and far between. Getting one solitary fix on a U-boat simply put a coloured pin into a big plotting table. From that there was no telling which way the submarine was heading. Was it outward-bound, with a full complement of torpedoes, or was it limping home with engine troubles? Or was it part of a ‘rake’ of other U-boats across the expected route of a convoy? The Submarine Tracking Room – using all its resources – tried to answer such questions, often guessing right and telling transatlantic convoys to change route and avoid the places where the U-boat packs were waiting. This rerouting of convoys was to become the most effective counter to the U-boats, and – since signals avoided all references to German movements – it was unlikely to reveal British successes with Enigma.
By 1941 the German armed forces had thousands of Enigma machines in use. One of the disadvantages to such machines was that they could be lost or stolen, and so could the keys, the settings for rotors and plug boards. Ever since the remarkable luck of finding some Enigma settings in the patrol boat VP2623, captured off Norway long before in April 1940, the codebreakers had been crying out for more.
On 23 February 1941 during a commando raid on the Lofoten Islands, northern Norway, the destroyer HMS Somali fought off a suicidal attack by a tiny German trawler, Krebs, which was left holed and beached. The Somali’s signals officer volunteered to search the little ship. From it he got some spare rotors and the Enigma ‘keys’ for the month of February. It was a splendid haul, more important to the war than the destruction of ships and factories and oil that had been the purpose of the commando raid.
It wasn’t the rotors found on Krebs that pleased the men at BP (Bletchley Park) – they already had them. The keys however were very valuable; with them current messages could be read without any delay. Even outdated keys were useful, enabling older messages to be examined. Such keys were always printed in water-soluble ink, and a dousing in seawater was enough to render them illegible. Ian Fleming, later to gain fame as the creator of James Bond, was at this time in naval intelligence and he came up with a hare-brained scheme to get some more of these keys. A captured airworthy German plane would be crash-landed in the sea and (it was hoped) found by a German ship. The rescued airmen would thereupon seize control of the ship and grab its codes. It says a lot about the desperate need for settings that this idea was taken seriously and a captured Heinkel made ready. Fortunately one of the boffins came up with a more practical adventure. The bounty of the February intercepts revealed that German weather-ships out in the Atlantic used Enigma. It also disclosed their movements. Why not capture one of those? The weather-ships were on station for months, so they might have longer lists of keys.
The destroyer Somali was used also in this engagement, which depended upon closing on the little weather-ships as quickly as possible in the hope that not everything would be tossed overboard. In the case of the weather-ship München the seizure and boarding went according to plan, and among the bundles of paperwork seized there were German Enigma keys for June. This would not enable the Bletchley Park men to read the whole of German naval traffic, for the navy had many different keys. But now the important ‘home waters’ radio traffic would be available. A second weather-ship, the Lauenberg, was intercepted on 28 June, just as the next month’s settings were due to come into use. Now traffic up to the end of July could be read.
By this time there had been another dramatic success in the story of Enigma. It was early morning on Friday 9 May 1941 and the outward bound convoy OB 318 was seven days out of Liverpool. There was reason for the British sailors to feel that the most hazardous part of the voyage was done; no U-boat had made a kill this far west. But trailing the convoy came U-110, one of the big long-range Type IX submarines. It was commanded by Kapitänleutnant Lemp, the man who sank the passenger liner Athenia in the first hours of the war. He now wore the Knight’s Cross – or ‘tin tie’ – at his collar. With him to the U-110 he had brought his cousin, who was regarded as a Jonah by the crew, after having two previous boats sunk under him.
In daylight, submerged, Lemp fired three torpedoes. Two merchant ships were hit. One ship’s stern tipped up so steeply that crates on her deck rolled into the ocean like ‘a child pouring toys out of