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Under the Prize Laws of 1936, passenger liners were to be immune from attack during times of war. Kapitän Leutnant zur See Fritz Julius Lemp in U-30 was not only well aware of the Prize Laws, but had received strict instructions that ships carrying passengers were not to be attacked. At 7:43 p.m., either in his haste to strike the first blow, or under the mistaken impression that the 14,000 ton passenger liner Athenia bound for Canada from Liverpool was a British Cruiser, Lemp loosed his torpedoes. 1300 survived; 22 of the 118 dead were United States citizens.
In rapid succession the Germans overran the Netherlands and Belgium. The French border was crossed on May 12. Allied forces were pushed back to Dunkirk, surrounded by the German armies. Believing Britain might sue for peace, and abetted by his Admirals' fear of the British Royal Navy, Hitler issued orders not to annihilate the Allied troops. In the week of May 26 to June 3, 345,000 troops were evacuated to England by a rag tag fleet of "anything that would float," although almost all their equipment had to be left behind. On June 22 France surrendered.
As far as Hitler was concerned, the War was over, and Britain would soon agree to a compromise peace. It took some time for him to realize that Churchill had no intention of anything but continued hostilities. Finally he agreed with Reichsmarshall Hermann Göring's confidence in an air offensive. In July and August a series of air raids were made against ports and air bases in England.
In August, codebreaking operations were physically moved to Bletchley Park (known familiarly as "BP"), an estate 40 miles from London, although its official designation was "Station X", as the tenth station. It was renamed Government Code and Cypher School (GC&CS, often irreverently referred to as the Golf, Cheese and Chess Society) under the direction of Naval Commander Alastair Denniston. A number of "huts" (small frame houses) were built to house the various divisions. Chess masters, mathematicians, professors and linguists were recruited from all over Great Britain, most from Cambridge University. Ian Fleming, one member of the team, went on to write the James Bond novels. A coding machine was featured in the James Bond movie "From Russia with Love." Not surprisingly, the brief view of the machine reveals it is nothing like an Enigma, since in 1968 the Enigma was still under wraps. In "The Secret Life of Ian Fleming," a 1990 movie, there is plenty of derring-do, but not a word about his work at BP.
This technique was used by the British to pinpoint the location of land radio transmitters in Germany. Widely spaced stations in England took bearings on the German transmitters. These bearings, plotted over a map of Germany, intersected at their locations. For some time the British had been monitoring German radio traffic, although they could read none of the coded messages.
Not all messages were in code; many of them were "chit-chat" between operators, trying to keep their stations operating properly. The coded messages were preceded by an unencoded preamble which identified the transmitting station, the receiving station, and time of day.
Much useful information was obtained through "traffic analysis," the study of radio traffic over the nets, and noting which messages went to whom. The French Bureau du Chiffre had been doing this effectively since World War I. This afforded an insight into the organization of the German armed forces. Frequently, individual operators could be identified by their unique "fist," the way they wielded their Morse keys. This often allowed the British to follow an individual operator when transmitting frequencies were changed every day at midnight.
Alan Turing, a brilliant mathematician who developed the "Universal Turing Machine," the conceptual forerunner of the modern digital computer, was also working in the same department.
Although Welchman was supposed to be working on traffic analysis, he idly started to think about how Enigma traffic might be decoded. From consideration of the doubly encoded "sub-keys" used by the Germans (see Chapter I), he devised a method of eliminating some of the many possible keys. A number of sheets were to be perforated with holes at specified locations, and stacked. Light shining through the holes in one or more locations could indicate possible keys. When he submitted his idea to Knox, he was surprised to find that the method was already in use! He had independently invented the Poles' Zygalski sheets, now known as Jeffreys sheets, named after the man in charge of the operation.
The possible keys suggested by the Jeffreys sheets were then tested on "bombes," machines descended from the Polish bomby. During the "phony war," with the French hunkered down on the Maginot line for seven months, BP was starting to decode some German messages. When Hitler invaded Denmark and Norway on April 9, 1940, much of the German traffic was being decoded.
Cillies and Kisses
Over the years, the British developed a number of codebreaking techniques.
One of the first relied on German operators using some easily remembered sequence of letters as rotor starting positions. There were identified as "Cillies", after one operator who frequently used "Cilly", his girlfriend's name.
Another was "Banburismus", invented by Alan Turing, and named after Banbury, where the forms were printed. It only indicated possible rotor settings, which were then fed to the bombes. It was a refinement of the Jeffreys sheet, searching for messages with the rotor positions close to each other.
Yet another was "Herivel Tips", named after John Herivel. It relied on lazy operators not resetting the settings at the start of a new shift.
Two identical messages in different keys were termed "kisses". By comparing the two messages, a foothold was obtained into the settings of the machines.
There were far more serious consequences, however. The German Atlantis had captured three British vessels, City of Baghdad, Benarty, and, on November 11, 1940, Automedon, from which they obtained the British merchant ship codes. With this knowledge their U-boats could be directed to sink ships supplying vital supplies to England.
B-Dienst had another source of information. Some American maritime insurance companies shared underwriting costs with their European counterparts. They regularly cabled ship manifests and routes to their offices in Switzerland. The Swiss, in turn, shared this information with their German co-insurers, providing the Germans with every detail of ship sailings and cargoes!
KNICKEBEIN KLEVE IST AUF PUNKT FUNF DREI GRAD ZWEI VIER MINUTEN NORD UND EINS GRAD WEST EINGERICHTET
(Bent-leg beam at Kleve is directed to the point 53° 24´ N. 1° W.; There are no number keys on Enigma; each digit had to be spelled out).
What was this bent-leg beam? The intelligence was passed on to the the appropriate authorities, who had also been informed of a conversation between two German prisoners discussing a new radio beam capable of guiding bombers to their targets.
The experts ridiculed such a possibility. Why would the Germans want to use such a complicated system, since navigation by the stars was sufficient for the RAF? (Actually, it wasn't, particularly under heavy clouds. In fact, the British had a terrible time finding their way over Germany and consistently missed their bombing targets). Churchill insisted that a search for the beam be instigated.
An airplane equipped with sensitive receivers located the beam, which passed directly over the Rolls-Royce factory at Derby, where engines for RAF fighters were manufactured! Ultra had achieved its first practical success. Countermeasures to jam the beams were soon developed, at first employing jury-rigged diathermy machines borrowed from local hospitals.
F. W. Winterbotham came up with SLUs, Special Liaison Units, small teams of junior officers briefed in Ultra, with a direct connection to BP. Not wishing to take chances that their own transmissions might be intercepted and decoded by the Germans, communication was at first by one-time pads. Later the RAF type X coding machine was employed. Although the Enigma machine is thoroughly discussed in the literature, there is a paucity of information on the Allies' machine. Presumably they were similar to Enigma, but employing a greater number of rotors and a more complicated stepping sequence. The Allies had an advantage in designing their machines, having thoroughly explored the weaknesses of the German system.
Safeguards were instituted
1. The number
of persons allowed to receive Ultra was strictly limited.
2. The SLU officer personally delivered messages to the commander, and destroyed them after they were read.
3. Ultra messages could not be transmitted or repeated.
4. Ultra was not to be used in any way whereby the enemy might guess the source; some cover story was necessary, for example, sending up a spotter plane even though the location of the target was known.
5. No recipient of Ultra could be placed in a position where he might be captured.
These rules were strictly adhered to although, as might be surmised, some problems arose later in the War when, for example, a British junior officer had to tell an American four star general what he could and could not do! As the conflict spread, SLUs were posted in locations all over the world, yet not once was Ultra compromised.
The concept of using convoys had been bandied about, but it was argued that there were insufficient escorts, and that collisions would abound.
Finally, the convoy system was adopted. The figure of one ship in ten sunk while sailing alone dropped to two out of a hundred. To counter the submarine menace depth charges and mines were developed, and air power in the form of planes and blimps were employed. In World War I, eleven million tons of shipping had been lost to submarines.
Großadmiral Erich Raeder, Commander in Chief of the Kriegsmarine, picked Commodore Karl Dönitz, a World War I U-Boat Captain, to command the U-Bootwaffe (submarine arm of the German Navy). Raeder knew that in 1939 the German Navy was no match for the British. Dönitz did not share Hitler's belief that Germany would not have to fight England, and lobbied hard to build up his U-Boat fleet. The Führer was more interested in building capital surface ships, however.
Although Dönitz had at first only ten U-Boats at his disposal, he maintained a close relationship with the officers and crews of his submarines, and was always solicitous of their welfare. He was able to weld them into an effective fighting force. September 17, 1939 Lt. Otto Schuhart's U-29 sank Aircraft Carrier HMS Courageous off the coast of Ireland. In a daring raid at Scapa Flow (the British Home Fleet anchorage), on October 13, Lt. Günther Prien's U-47 sank the Battleship HMS Royal Oak.
The Enigma rotors were given to various crew members, to be thrown into the ocean as they abandoned the sinking sub. In the excitement, one of the crewman forgot to jettison his, and the British found three rotors in his pants pocket after they had picked up the survivors.
Eight rotors, numbered I through VIII were in use in Enigma machines, but three (VI, VII and VIII) were used exclusively by the Kriegsmarine. VI and VII were recovered in this operation, but without rotor VIII the British were still in the dark as to Dönitz' messages to and from his U-Boats. Apparently, the British either solved or came into possession of rotor VIII, although how still remains a mystery.
The naval Enigma used the same number of rotors (three) as the standard Enigma until February 1, 1941, when they added a fourth rotor. At Dönitz ' insistence this was accomplished by replacing the umkehrwalze with a thinner one. There were two extra rotors called "beta" and "gamma". The fourth rotor did not rotate automatically in the scrambler, but could be set to one of 26 positions, one of which (Position "A") converted the machine to a 3-rotor machine, allowing Enigma to send and receive messages in either the standard mode, or the special Kriegmarine code. The British dubbed these transmissions "Shark".
It took almost a year to break into this key, with ship convoy sinkings rising dramatically. Finally, by the end of the year, the wiring of the special wheels was solved, by comparing duplicate messages sent in the two systems.
In September, Dönitz formed his U-boats into "wolf packs," assembled and controlled by two-way radio messages. From B-Dienst information, and submarine position reports radioed back to his headquarters, he could decimate the vital convoys. The British had at their disposal ASDIC submarine detection equipment, which was not very effective. In a joint French-British venture between World Wars, a submarine detection device was developed to bounce sound waves off submerged submarines. The returning echo was picked up by a receiver. The English version was named ASDIC (Anti Submarine Detection Investigation Committee); the Americans called it SONAR (SOund NAvigation Ranging). In practice, results were disappointing; the narrow beam could often be avoided, and there was no indication of the depth of the target. The device was equally adept at locating rocks, whales, schools of fish and thermoclines (boundaries between layers of different water temperatures and salinities). Lack of escort vessels and patrol aircraft also limited anti-submarine warfare.
Between June and July Kapitänleutnant Günther Prien's U-47 in one month sank eight ships totaling 66,588 tons. On a single patrol Lt. Otto Kretschmer in U-99 sank seven ships totaling 65,137 tons (he went on to become the highest-scoring U-Boat Commander of World War II, with 44 ships and 266,269 tons to his credit). From July to October 217 ships and 1,111,185 tons went to the bottom. Britain's life line was in serious danger of being severed.
Göring assured the Führer that his planes could sweep the RAF from the skies, giving Germany total air control over the Channel. In fact, he went so far as to inform Hitler that a cross-channel invasion would not be necessary; his Luftwaffe alone could force the British to capitulate. By mid-July BP decoded a message from Göring informing his Generals of Operation Sealion.
A flood of messages followed which, once decoded, revealed squadron strengths and their locations in Holland, France and Belgium. Some 1300 bombers would be available for the assault, and parachute troops were being assembled. Ultra picked up a variety of messages. One was an order for troops to be deloused prior to Göring's inspection tours!
Finally, on Sept. 5, with only half of his aircraft still serviceable, Göring made a fatal mistake. Had he concentrated his attack on RAF bases, he might have finished them off. However, he opted for a 300 bomber raid on the London docks, hoping to lure the RAF to their destruction. It didn't work.
Although the bombings continued, on Sept. 17 Ultra decoded a signal ordering loading equipment at Dutch airfields dismantled - Sealion had been canceled.
However, the blitz of London continued into the winter of 1940, and was extended to other cities as well. If England couldn't be invaded, perhaps it could be bombed into submission.
Leigh-Mallory, not apprised of Ultra information, chafing at the bit from inaction in his sector, and not realizing that his aircraft were being held in reserve, promulgated the "Balbo", (Named after Italo Balbo, Air Minister of Italy from 1929 to 1933, who first proposed it) in which all available aircraft were to be combined into formidable wings, to attack the Luftwaffe en masse, as opposed to being committed individually. Group 12 would have had more time to implement this plan, but Group 11, closer to the enemy airfields, would not have had that advantage. Furthermore, the British, with their limited resources, were much more effective if pitted individually against the large, unmaneuverable flights of bombers.
Lewin, in Ultra Goes to War (1978) refutes this account, claiming that the message referred to "Korn", the German code word for Coventry, which was not known to the English. Thus, there was no reason for them to believe it was Coventry.
To obtain advance weather information the Germans stationed converted fishing trawlers northeast of Iceland. Observations were made of temperatures, wind direction, etc. These were encoded into the "short weather cipher," in which a single letter stood for a particular temperature, barometric pressure, etc.
The British decided on a bold plan to capture a weather ship's secret documents in the hope it might disclose information useful in decoding naval messages. Would the Germans put the Naval key on a weather ship? And if one were captured, wouldn't the Germans be warned, immediately change their keys, and possibly even the rotor wiring?
Feb. 22, 1941 the British recovered the rotors and keys for February through May from Krebs, a trawler converted into a patrol boat, off the coast of Norway. On May 7 a small British task force captured weather ship München. The crew were able to fire off a message that they were being pursued. On June 25, weather ship Lauenberg was also captured. In none of these operations was an Enigma machine captured.
In spite of the loss of these three ships, not to mention the message from München, the Germans did not change their keys. Perhaps they thought the keys had been lost with the ships, or they may have had other, more important matters on their mind.
Cdr. A. J. Baker-Cresswell, aboard destroyer Bulldog almost rammed the submarine, but was able to stop short when he realized he might be able to capture the U-boat intact.
The scuttling charges failed to explode, and the British were able to board. Radioman 3C Heinz Wilde, indoctrinated to believe that Enigma was iimpregnable even if captured and, under the impression that the vessel was about to sink, had made no provisions to destroy the Enigma machine or the keys. The British recovered everything - the Naval Enigma with its rotors, the vital keys through June, and position charts. There are two versions of what happened to Lemp. In one, realizing that he had given the British a vital key to Kriegsmarine operations, he committed suicide by drowning himself. In another, he was shot by the British as he attempted to reboard his ship in an attempt to sink it himself.
An attempt was made to tow the captured sub back to England but it sank the next day. This was fortuitous; to Dönitz it appeared that U-110 had vanished without a trace, and there was no reason to believe that the Kriegsmarine codes were no longer secure.
There was a problem, however. The Germans referred to locations by a grid coordinate system, with which the British were not familiar. Ever resourceful, they came up with "gardening", a technique whereby mines were laid in the North Sea. The German warning messages located the mines using their own grid system. With this information and knowing where they were sown, the German grid locations were solved.
Using the captured keys for May and June, the British were able to locate and sink cargo ships and tankers supplying U-Boats working the South Atlantic.
By the winter of 1940-41, England was perilously close to defeat. Knowing every detail of the enemy's plans was not enough. There were not enough men, machines and supplies.
Ultra may have tipped the balance in the Battle of Britain, but there were to be other trials ahead. Her vital supply lines were in danger of being severed, and the United States was complacently ignoring the whole affair.
It was going to be a very close shave, indeed.
Go to Chapter 3
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