Kitabı oku: «Blood, Tears and Folly: An Objective Look at World War II», sayfa 6

From the water Lemp watched the British go aboard his command. Realizing that his detonators had failed and knowing that he was responsible for the destruction of the Enigma machine and all the secret material, he seems to have deliberately allowed himself to drown. (Ex-U-boat men – and at least one account²⁴ – say that Lemp swam back to the U-boat to sink her and was shot by the British boarding party as he climbed on to the deck, but I find no evidence to support this allegation.)

HMS Bulldog’s captain tried to tow the U-boat back to port but failed. He showed masterly restraint and impeccable good sense in keeping his extraordinary success secret, so that no news of it could leak back to German intelligence, but he little knew what a tremendous coup he had brought off. The men from BP had never had such a wonderful collection of data: a new machine, spare rotors and a list of the prescribed rotor settings for the length of the U-boat’s cruise – three months – and a mountain of helpful material that enabled them to read most Enigma machine messages in the code Hydra for the rest of the war. It also helped with the big warship code Neptun and the Mediterranean codes Sud and Medusa.

The ups and downs of the Enigma struggle meant that messages were sometimes read almost immediately and at other times there were long delays. Most messages were never read. The naval Enigma was the most difficult to crack and many successes came from captured current German keys. Without such helpful clues the German naval secrets could seldom be tapped. And yet it was only because Bletchley Park had been set up with its Enigma machines and bombes that the captured keys could be used.

But Enigma was only one part of the Atlantic battle. Nothing was more decisive than the rate at which merchantmen and escorts could be constructed in British and North American shipyards. The construction of U-boats was equally telling, and so were the global demands that took warships and U-boats to other parts of the world. The weather played a part, and so did the successes of the German B-Dienst, the service which intercepted British signals. The availability of Allied air cover and of long-range aircraft, and, the extent of Luftwaffe reconnaissance and anti-shipping operations, influenced the monthly figures, as did the operations of German surface raiders. The rationing of food and petrol was vital to the struggle, as was the improving technology of anti-submarine weapons – such as the hedgehog depth-charge thrower – and the use of better explosive charges. Just as deadly in effect were airborne and shipborne radar and, perhaps most important of all, ‘Huff Duff’, which provided ever better ‘fixes’.

The Germans never suspected that the British might be reading their Enigma traffic on a regular basis. The chief of the German navy’s Signals, and the head of the Naval Intelligence Service, assured Dönitz that it was not possible to crack such machine codes. After the war Dönitz still believed them. To some extent of course this was true.

By 23 June 1941 British penetration of the Hydra traffic had given the OIC (Operational Intelligence Centre, of which the Submarine Tracking Room was a part) a great deal of supplementary data, including details of all German inshore traffic and thus minelaying operations, as well as the routine messages that marked the beginning and end of a U-boat’s cruise.

Enigma intercepts also revealed the positions of five tankers, two supply ships and a scouting ship positioned for the commerce-raiding cruise by Bismarck and Prinz Eugen. When plans were made to attack these auxiliary vessels, the navy decided to leave two of them – the tanker Gedania and the scout Gonzenheim – unmolested. To attack them all might prompt the Germans to guess their Enigma had been penetrated. By chance the Royal Navy happened upon those ships too, and so the whole lot was sunk. As feared, this massacre – five of the sinkings occurring over a three-day period – made the Germans investigate the possibility that Enigma was insecure. They decided that the spate of sinkings was probably a coincidence, but additional security measures were introduced just to be on the safe side.

One of the planned measures was a fourth rotor for the navy’s Enigma machines. A shiny new Enigma machine had been recovered from U-570, which in August 1941 surfaced near Iceland and fell victim to an RAF plane. The Enigma machine had been built with an extra window, all ready for the extra rotor when it was issued. The sight of it sent a shudder through the personnel at BP, for the mathematicians calculated that it would multiply their already Herculean task by a factor of 26! They were right: 1942 brought the four-rotor machine and a year of darkness for the men peering into the German navy Enigma. Sinkings went from 600,000 tons in the second half of 1941 to 2,600,000 tons in the second half of 1942.²⁵

A last word about Bletchley Park is a cautionary one. Considerable opportunities for intelligence gathering were neglected because the pre-war SIS took no interest in foreign radio transmissions other than messages. It wasn’t until 1940 that there was any attempt to intercept or analyse radar or radio navigation signals. GC&CS was responsible not only for cryptography and communications intelligence but also for safeguarding British communications. Whatever its glittering, and much trumpeted, successes at the former, its role as guardian was a chronic and dismal failure.

The Submarine Tracking Room

The Submarine Tracking Room used a wide range of incoming data. Anything that could possibly help was funnelled here. For the admirals perhaps the most disconcerting thing about this place, where Britain’s most vital battle was being fought and from which came the operational decisions that sent orders to the warships, was that by 1941 no regular naval officer was anywhere to be seen.

The room was run by Rodger Winn, a 30-year-old lawyer with degrees from Cambridge and Harvard. He had drifted into this job as a civilian, after volunteering to interrogate enemy prisoners. Winn would never have passed a Royal Navy physical examination: childhood polio had left him a hump-backed cripple who walked with a limp. Neither would he have found favour in the peacetime navy, for he had limited respect for authority. Like many barristers he was a talented story-teller with a sharp tongue. The security of having a well paid profession waiting for him encouraged him to stand firm against authority. When a decision of Winn’s was challenged by an admiral, Winn put a vast heap of reports, sightings, charts and intercepts on to the admiral’s desk and politely asked him for his solution.

When Winn joined the Tracking Room staff, the emphasis was on plotting the present state of the Atlantic battle, rather than predicting the future. But such was Winn’s talent for reading the minds of the U-boat men, that in January 1941 his boss was moved out of the Tracking Room and Winn was given sole command of it and made a commander in the Royal Navy Volunteer Reserve. And when in January 1942 he chose an assistant, it was another ‘civilian’, a bespectacled insurance broker from Lloyd’s.

Most of the Tracking Room’s floor space was occupied by a seven-foot-square plotting table depicting the North Atlantic. It was covered with sheets of white paper and brightly lit from above, like a billiards table. Pins showed the progress of the convoys on their two-week voyages across the ocean, while others showed the U-boats on their month-long sorties. All the evidence of U-boat activity – radio fixes, sightings, signals and sinkings – was written in pencil on to the paper table cover. The coloured pins revealed the source: red-topped pins for a fix, white for a sighting, blue for Enigma intercepts. Red lines showed the extreme limits of air cover. A cluster of pins showed where a convoy was at that moment under attack by a wolf pack.

Another large table was covered by a captured map to show the German navy grid. There was also a map showing the Huff Duff stations that took bearings on U-boat radio messages. Strings could be stretched across the map to intersect. A ‘good fix’ was within 40 or 50 miles, a ‘very good fix’ meant within 10 to 15 miles. On one notable occasion a U-boat was found within three miles of its fix in the Baltic, and sunk by a Coastal Command plane, all within 30 minutes of the U-boat’s tell-tale radio transmission.²⁶

The walls of the Tracking Room were covered in charts and graphs showing such things as U-boat sinkings and estimated production. There were pictures too, including a photograph of Dönitz. Winn tried to make this room as he imagined Admiral Dönitz had his operations room.

Each day at noon the information from the table was translated into a situation report. The most vital parts of the plot were used each day to update Churchill’s map in the War Room. Once a week, during the night, staff renewed all the white paper sheets on the plotting table, carefully transferring all the current data to them. The Submarine Tracking Room became a favourite place to take VIPs. For extra security the plotting table used coded references so that visitors would not get an accurate or complete view of what was happening.

Around the Tracking Room there were offices for the watchkeepers. Winn’s office had a glass front so that he could see the civilian watchkeepers plotting the convoys while RNVR officers (wearing mufti) plotted the enemy movements. Civilian day-workers kept the records and card indexes. A nearby office held telex machines connected by direct line to Bletchley Park. Arriving Enigma messages were brought into the Tracking Room by a Wren (Woman’s Royal Naval Service) who was called ‘the secret lady’.²⁷ One of the tasks of the Tracking Room staff was to compile an account of each new U-boat. Such a record might start with the low-grade radio traffic sent while the new boat was working-up in the Baltic. From that time onwards every possible detail of boat and crew would be filed for reference. Names, sinkings, medals and commendations, damage and refits were all noted.

Because the Royal Navy gave most of its officers sea duties between spells at a desk, the plotting table often showed the hazards of friends who had recently worked here. One officer, Commander Boyle, was well known to the men in the Tracking Room and was married to a secretary who worked there. He was escort commander for a convoy of eleven tankers and his friends watched the plot day after day as its ships were picked off one at a time. Finally only one ship survived but Boyle was saved.²⁸

By using his background material, and watching all the movements on the plotting table, Winn made decisions about re-routing convoys or even detaching precious warships if the situation required it. Each morning he phoned to the Western Approaches Command in Liverpool and spoke with RAM Coastal Command too. When Enigma material was available, it made Winn’s job incomparably easier. Often he phoned directly to those other civilian boffins at Bletchley Park and asked them to keep a lookout for messages with some known component.

B-Dienst

The German navy’s Observation and Cryptanalytic Service, Beobachtungs und Entzifferungs Dienst, was housed at 72 Tirpitzufer, Berlin. In the first two years of war there is no doubt that the German navy gained more advantage from the intelligence provided to them by their Beobachter-Dienst than did the Royal Navy from the Enigma work at Bletchley Park. The men of the German navy’s B-Dienst (modelled after the Royal Navy’s Room 40) had been listening to British fleet signals long before war began, and they broke the British convoy code (BAMS: British and Allied Merchant Ship Code) without difficulty. The Germans could read a great deal of the Royal Navy traffic too, and Dönitz planned his Atlantic operations upon the wealth of material he got from B-Dienst.

The British Admiralty had resisted the idea of having coding machines. The Typex, resembling the Enigma, had been offered to them but was turned down. One would have thought that a sample of what a potential enemy was using might have been recognized as a worthwhile investment. Lord Louis Mountbatten, when still a Lieutenant-Commander, had drawn attention to the weakness of the whole system of Royal Navy codes and was ordered ‘to mind his own business’.²⁹

The Royal Navy’s refusal to use ciphering machines made it easier for the Germans. Even the convoy designations gave vital information: ONS was a slow outward-bound convoy to North America (Nova Scotia); HX homeward bound from Halifax. From such tags it was possible to guess the routes, and merchantmen were listed by name with a short description of their cargo: war material, eight aircraft on deck, locomotives on deck, chemicals, machine parts. Thus Britain’s most critical supply convoys were exposed to attack and continued to be so until the codes were changed in the summer of 1943.

All the same the U-boat commander’s task was not an easy one. The convoys maintained radio silence most of the voyage. On a clear day, an alert lookout on a submarine conning-tower might spot a convoy’s smoke (against clear sky or cloud) at 50 miles. In calm seas, and at the right depth, a submarine’s hydrophones might pick up the sound of a convoy at the same distance. Yet endless chivvying by the convoy commodores discouraged smoke, and the North Atlantic’s clear days, and calm days, are not numerous. Lookouts, even German lookouts, are not always alert. We can therefore think in terms of a 25-mile visibility or less.

Always we must remember the speeds at which the opposing units could travel. It has been nicely depicted by a historian who suggested that we think of the Atlantic in terms of European distances: a U-boat in Vienna is told to attack a convoy in London. On the surface he can move at the speed of a pedal cycle, submerged he will go at approximately walking pace. Then we understand why convoys sometimes escaped intact, despite the men of B-Dienst.

4
SCIENCE GOES TO SEA

Do you really believe that the sciences would

ever have originated and grown if the way had not been

prepared by magicians, alchemists,

astrologers and witches …

Friedrich Wilhelm Nietzsche

In the opening days of the war, the German magnetic mine gave the Royal Navy one of its first big shocks. It was a simple weapon, but the method of its activation demonstrated some of the curiosities of the natural world. The mines sat on the sea bed and came to the surface to explode against the hulls of ships that passed over them. Inside each mine there was a ‘dip needle’ which was pushed down by the ‘downwards north pole’ of the ship passing over it. Such mines were activated only by ships built in the northern hemisphere. Ships built south of the equator had a ‘downwards south pole’ which pulled the contacts further apart, so they could pass quite safely over magnetic mines.

In fact it was more complex than that: the magnetism of a ship’s hull was not simply north or south. Each ship was different. The hulls varied according to the direction, relative to magnetic north, in which the ship’s keel had been laid down when built. Even more surprisingly, it was discovered that ships sailing to the southern hemisphere and back again changed their ‘magnetic signature’. Prefabricated ships were sometimes assembled from two halves made in different places; the halves then had different magnetic properties. Once a ship’s signature was known, it could be demagnetized by means of a fluxmeter. When the threat of the magnetic mine was suddenly understood, Britain’s only manufacturer of fluxmeters was asked to supply 500 on a rush order; before that only a dozen had been made since 1898.

By their nature these ‘influence mines’ were restricted to use in shallow water, the type TMB in 15 fathoms and the TMC no deeper than 20 fathoms. Smaller mines could be laid through the U-boat’s torpedo tubes; three of them together were about the length of a torpedo. Laid by U-boats or parachuted from low-flying aircraft into harbours, estuaries and coastal sea routes, the German mines caused consternation. The battleship HMS Nelson and the cruiser HMS Belfast were seriously damaged by mines, three destroyers were sunk and so were 129 merchant ships. The Thames Estuary became so littered with German mines that there was talk of closing down the Port of London.

It seemed at first as if it was a problem easily solved, since the Royal Navy had used magnetic mines in 1917. In the interwar years Admiralty scientists had experimented with the magnetic properties of ships’ hulls, but the emphasis was upon counter-measures to the magnetic torpedo. This meant a powerful magnetism that would prematurely explode a torpedo as it approached. But scientists and technicians were few in number and their work was overruled by officials at the Admiralty who thought that mines, like submarines, were weapons for inferior naval powers. Dusting off their old research, the navy tried it out. But they found that magnetic sweeps that countered British magnetic mines exploded German ones. The sweeping devices were often destroyed and sometimes mine-sweepers were badly damaged.

The night of 22/23 November 1939¹ was dark and moonless. Between 9 and 10 pm a Heinkel He 111, following the Thames Estuary, flew very low over the tip of Southend pier. It was a good landmark: probably Luftwaffe crews were briefed to use the pier as a navigating fix. A machine-gun team at the pier’s far end opened fire and saw two parachutes fall from the plane. Startled by the unexpected gunfire, the Germans had dropped two mines into the shallow tidal water. Its load lightened, the Heinkel sped away.

The report that men had jumped out of the aircraft was discounted. Before midnight, Churchill was told that there was probably going to be a chance to examine the new weapon. By 1.30 am on that same night two experts briefed by Churchill, and the first sea lord, were on their way by car to Shoeburyness, where the mines were exposed by the outgoing tide. By 4 am – with rain falling heavily – the investigating team was out on the exposed mud-flats. Using a powerful portable signal lamp, they were looking at a black aluminium cylinder, seven feet in length and about two feet in diameter. Before anything much could be done, beyond securing the mines, the incoming tide had swallowed them out of reach until the following afternoon.²

Next day steel-nerved technicians from HMS Vernon (the RN’s mine school) defused the weapon. By a stroke of fortune, a mechanical device to keep the mine safe until it had settled on the seabed had jammed. It was actuated by the technicians rolling the mine over but by that time the mechanism had been rendered safe. Stripped of its detonators and priming charges the mine was taken for examination to a ‘non-magnetic laboratory’. In a matter of hours the new weapon was understood: it operated on a vertical magnetic field and required about 50 milligauss to fire it. The threat remained.

When, on Saturday morning, Rear-Admiral W. F. Wake Walker told government scientist Frederick Brundett about the capture of the mine and that he would need twelve engineers by Monday morning, Brundett drove to the south coast to seek out individually men with special engineering skills and sign them up on the spot. One whom he considered essential was already being paid £2,000 a year. ‘As it happened the Director of Scientific Research at the time was only getting about £1,700 a year, and I was subsequently told by the Treasury that I couldn’t do it. I pointed out that I’d already done it and that he was in fact already working for us.’³

Some anti-mine experiments were performed by sailors who towed toy ships backwards and forwards over cables in ‘canoe lake’, a children’s boating pool in Southsea, near to HMS Vernon. Various counter-measures were devised and put into operation immediately. These included ‘de-gaussing’, which neutralized the vertical magnetism of a ship. The mines could be swept by floating electrical cables (through which a current pulsed) behind a de-gaussed ship. Large coils were also installed in low-flying aircraft as a quick way to neutralize minefields.

Such measures were not enough to solve the problem completely. Channels swept by aircraft were narrow and unmarked. The German aviators were bold: one minelaying seaplane landed in Harwich harbour, carefully placed its mines, and then took off again. It was the minelaying operations of low-flying aircraft that led to the construction of new radar stations with apparatus designed for low-level detection. When the Battle of Britain began, these stations were to play a vitally important part in detecting low-flying formations that would otherwise have got in under the radar screen.

The de-gaussing that all British warships were given at this time probably saved some of them from attack by magnetic torpedoes, notably during the Norwegian campaign. At the time these failures were considered to be due to faults in German torpedoes, and no one can be sure of what exactly happened inside the warheads.

The Germans hit upon the idea of sowing mixed minefields with both magnetic and moored mines. These required tricky sweeping techniques. They reversed polarity to catch ships that had been ‘over-de-gaussed’. Delayed-action fuses kept the mines inactive for a period; thus sweeping would be without result.

Then came acoustic mines, which had to be swept with noisy ‘hammer boxes’. There were double fuses that would work only when two triggers were activated, such as noise and polarity. But by the summer of 1940 the magnetic mine had ceased to be a real danger.

On 7 May 1940 a new threat arose. A modified version of the BM 1000, intended as a sea mine in the Clyde, overshot and landed on the Clydeside hills near Dumbarton. These ingenious dual-purpose ‘bomb mines’ were fitted with Rheinmetall inertia fuses when used against land targets. Falling into water at least 24 feet deep they functioned as a magnetic mine; on soft mud or in shallow water they would self-destruct. They would also self-destruct (by means of a hydrostatic valve) when the water pressure lessened, as it would when they were lifted to the surface. It was an example of German thoroughness that, despite all the foregoing precautions, the BM 1000 also incorporated one of the most cunning booby traps ever built. A set of photo-electric cells connected to a detonator would explode the bomb if light got inside it. This was a way of killing any bomb team who got to see the workings. By amazing luck, the bomb found at Dumbarton had suffered a circuit failure.⁴

A few months later this sort of bomb-mine was extensively used during the night bombing of London. They parachuted down and caused widespread destruction without forming a crater. Londoners found it easy to recognize the results and called them ‘land mines’.

The menace of the magnetic mine had been overcome by the scientists, and this was the important fact. Before the war the admirals and generals in Whitehall had showed little interest in science and technology, but success with the magnetic mine changed that attitude. According to Dr C. F. Goodeve, who was a physicist and RNVR officer: ‘it was the first technical battle in which we won a decisive victory over the enemy; but more important still, it was one which brought science fully into the war in the very early days’.⁵

In Germany the Nazis had broken with the nineteenth- and early twentieth-century tradition of political encouragement and social respect for science and its practitioners, and there was little or no collaboration between the scientists and the military until the end of 1943, when German scientists were invited to help with the Battle of the Atlantic. Even then they were simply asked to identify Allied radio and radar transmissions.

But Nazi distrust of science and top-level obstruction of research did not change the way in which German industry employed men who knew how to apply science and engineering to design and production. The magnetic mine provides a good example of the excellence of German design. The only reason for the mine’s failure to cripple British shipping was that Germany went to war with only 1,500 of them in stock. After the first sequence of minelaying operations, the Germans had to wait until March 1940 for more to be manufactured.⁶ It was this respite that saved Britain’s defences from being overwhelmed, and provided an interval during which the menace could be countered.