A Brief History of Science with Levity Page 9

  Based on pulsed transmissions as used for probing the ionosphere, a preliminary system was designed and built at the RRS by the team. Their existing transmitter had a peak power of about 1KW, and Wilkins had estimated that 100KW would be needed. Edward George Bowen was added to the team to design and build such a transmitter. Bowen’s transmitter operated at 6MHz, had a pulse repetition rate of 25Hz, a pulse width of 25μs, and approached the desired power.

  Orford Ness, a narrow, 19-mile (31km) peninsula in Suffolk along the coast of the North Sea, was selected as the test site. Here the equipment would be openly operated in the guise of an ionospheric monitoring station.

  In May 1935, the equipment was moved to Orford Ness. Six wooden towers were erected; two for stringing the transmitting antenna, and four for corners of crossed receiving antennas. In June, general testing of the equipment began.

  On 17th June, the first target was detected by a Scapa flying boat at 17 miles (27km) range. On this date, radio-based detection and ranging was demonstrated for the first time. Watson-Watt, Wilkins and Bowen are generally credited with initiating what would later be called radar.

  In December 1935, the British Treasury appropriated £60,000 for a five-station system for Chain Home, covering approaches to the Thames Estuary. The secretary of the Tizard Committee, Albert Percival Rowe, coined the acronym RDF as a cover for the work, meaning Range and Direction Finding but suggesting the already well-known Radio Direction Finding.

  Late in 1935, responding to Lindemann’s recognition of the need for night detection and interception equipment, and realising the existing transmitters were too heavy for aircraft, Bowen proposed fitting only receivers to aircraft. In 1937 Bowen’s team used their crude ASV radar, the world’s first airborne set, to detect the Home Fleet in dismal weather. Only in spring 1939, “as a matter of great urgency” after the failure of the searchlight system Silhouette, did attention turn to using ASV for air-to-air interception (AI).

  Demonstrated in June 1939, AI got a warm reception from Dowding, and even more so from Churchill. However, its accuracy, depending on the height of the aircraft, meant CH was not accurate enough to place an aircraft within its detection range, and an additional system was required. Its wooden chassis also had a disturbing tendency to catch fire (even with attention from expert technicians).

  In 1940 John Randall and Harry Boot developed the cavity magnetron which made 10cm radar a reality. This device, the size of a small dinner plate, could be carried easily on aircraft, and the short wavelength meant the antenna would also be small, and hence suitable for mounting on aircraft. The short wavelength and high power made it very effective at spotting submarines from the air.

  To aid Chain Home in making height calculations, at Dowding’s request, the Electrical Calculator Type Q (commonly called the Fruit Machine) was introduced in 1940.

  The solution to night intercepts would be provided by Dr W. B. Lewis, who proposed a new, more accurate ground control display, the Plan Position Indicator (PPI), a new Ground Controlled Interception (GCI) radar, and reliable AI radar. The AI sets would ultimately be built by EMI. GCI was unquestionably delayed by Watson-Watt’s opposition to it and his belief that CH was sufficient, as well as by Bowen’s preference for using ASV for navigation, despite Bomber Command disclaiming a need for it, and by Tizard’s reliance on the faulty Silhouette system.

  In March 1936 the work at Orford Ness was moved to Bawdsey Manor, nearby on the mainland. Until this time, the work had officially still been under the DSIR, but was now transferred to the Air Ministry. At the new Bawdsey Research Station, the CH equipment was assembled as a prototype. There were equipment problems when the RAF first tested the prototype station in September 1936. These were cleared by the next April, and the Air Ministry started plans for a larger network of stations.

  Initial hardware at CH stations was as follows: the transmitters operated on four pre-selected frequencies between 20 and 55 MHz, adjustable within fifteen seconds, and delivered a peak power of 200 KW. The pulse duration was adjustable between 5 to 25μs, with a repetition rate selectable as either 25 or 50Hz. For synchronisation of all CH transmitters, the pulse generator was locked to the 50 Hz of the British power grid. Four 360-foot (110-metre) steel towers supported transmitting antennas, and four 240-foot (73-metre) wooden towers supported cross-dipole arrays at three different levels. A goniometer was used to improve the directional accuracy from the multiple receiving antennas.

  By the summer of 1937, twenty initial CH stations were in operation. A major RAF exercise was performed before the end of the year, and was such a success that £10million was appropriated by the Treasury for an eventual full chain of coastal stations. At the start of 1938, the RAF took over control of all CH stations, and the network began regular operations.

  In May 1938, Rowe replaced Watson-Watt as Superintendent at Bawdsey. In addition to the work on CH and the successor systems, major work was now being performed in airborne RDF equipment. This was led by E. G. Bowen and centred on 200MHz (1.5 metre) radio sets. The higher frequency allowed smaller antennas, appropriate for aircraft installation.

  From the initiation of RDF work at Orford Ness, the Air Ministry had kept the British Army and the Royal Navy generally informed. This led to both of these forces having their own RDF developments. We will now look at the development of ASDIC, a scientific breakthrough that played a major part in the success of the Battle of the Atlantic.

  ASDIC was the primary underwater detection device used by the Allied convoy escort ships throughout World War II. The first crude versions were created towards the end of World War I, and further developed in the following years by the Royal Navy.

  ASDIC, known to the Americans as sonar, was basically a transmitter-receiver sending out a highly directional sound wave through the water. If the sound wave struck a submerged object it was reflected back and picked up by the receiver. The length of the time from transmission until the echo was received was used to measure the range, which was shown as a flickering light on the range scale. By mounting the transmitter head so that it could be directed almost like a searchlight, the bearing of the target could be read from the compass receiver.

  The transmitter (sound) head extended beneath the ship, and was encased in a large metal dome to minimise the noise of the water rushing past the ship while at moderate speed. This dome was filled with water, through which the sound passed, although this water was stationary and acted almost like a bumper. Noise levels remained relatively low at moderate speeds, but anything above 18 knots resulted in too much noise, and good contacts were difficult to find. The same problems also resulted from bad weather when the ships were rolling, pitching and heaving.

  During screening operations, the ASDIC operator searched through an arc of roughly 45 degrees each side of the base course of the vessel. The ASDIC had to be stopped at regular intervals on this arc for long enough to allow the relatively slow underwater sound waves to return should they locate a submerged target. Normally the head would be stopped on a bearing and a sound pulse would be transmitted, which would be heard as a “ping” noise. If no echo was received after several seconds the head would be rotated a few degrees (usually five), and the process repeated throughout the watch.

  If the outgoing impulse stuck a submerged target, the echo would be heard as a distinct “beep”. If this occurred, the ASDIC operator would sound the alarm, feed the range and bearing to the bridge, and then immediately start left and right cuts to try to determine the width of the target and try to see if it was moving from one side to another. He could also determine if the target was closing or opening the range.

  Echoes would bounce back from many things besides the U-boats, such as whales, schools of fish, vertical sea currents and ship’s wakes. This caused many false alarms, especially with inexperienced operators. The veteran operator was much better at figuring out these bad signals and hunting down the intended target. The commanding officers quickly learned which operators wer
e the most reliable.

  Another problem was that often a real U-boat could not be detected due to water conditions. ASDIC was not very reliable in rough water, nor when layers of different temperature deflected the sound waves. U-boats could dive beneath such layers to avoid detection. Modern nuclear and diesel submarines use this tactic to this day.

  The device could also be used to listen as well as pinging. The propeller noises of the U-boat would sometimes be heard, as well as the noises from the operation of various types of machinery on board, such as its use of the compressed air in the ballast tanks to change depths. This detection method was unusual, as one of the standard German tactics, when located, was to dive deep, rig for silent running and hide beneath a thermal layer at speeds slow enough to eliminate any cavitation from the propellers.

  When the U-boat was located, the attacking vessel would rush directly towards the contact, usually at a speed of 15 knots. This run was used to determine the final movements of the target, and to further plot the final attack. The attacking vessel had to be fairly sure where the U-boat was, and estimate where it would be when the depth charge reached its calculated depth. Thus the attacking vessel would have to take a lead on the U-boat, much as a hunter does on a bird. At 500 metres the Allied commander hoped to know what the U-boat was doing, and then he finalised his attack.

  As the range closed, the U-boat would pass under the beam of the ASDIC and be lost to the escort. The deeper the U-boat was, the longer the range of the lost contact was, and it was thus more difficult to attack accurately. Normally a good and firm contact was lost at 300 metres. This did not affect the forward-launched Hedgehogs as much as the depth charges.

  Even if the attack was delivered with the correct lead angle and firing time, there was no guarantee of damage to the U-boat since its depth could differ from the settings at which the depth charges were set to explode. The correct depth of the U-boat could only be guessed or estimated based on the range at which contact was lost.

  The U-boats, of course, used tactics to evade the depth charges and Hedgehogs. The best time to act was when the attacking vessel had taken its lead angle and the ASDIC contact was just lost.

  A very common German move was to run away from the escort and force it on a stern chase, pinging through the wake of the U-boat, which could give the ASDIC a hard time. Then at the moment of the ASDIC losing contact, the U-boat would take a radical turn to the left or right, and more often than not escape out of the attacking pattern.

  Another tactic was to turn radically with great power and disturb the water in order to confuse the ASDIC, and sometimes causing the attacker to be shaken off. The Germans also often released chemical pellets, which would produce clouds of bubbles to reflect the sound waves of the ASDIC.

  Yet another tactic was to dive very deep, under a thermal layer or beneath the depth at which depth charges were normally set to explode. From 1942 onwards, depths of 200 meters (over 600 feet) were not uncommon in an evasive tactic.

  CHAPTER 10

  While writing this book, I asked some friends to proof read various sections. A good friend of mine, who is a retired English teacher from Melbourne, made me laugh, as he said that I must be careful not to turn the book into an autobiography. I commented that I was simply trying to include some amusing incidents that have happened to me during my life in order to lighten the heavier scientific parts of the book.

  He then told me about the rumours of Mick Jagger’s autobiography. He said that some years ago, Mick Jagger was allegedly paid £50,000 as an initial down payment for his memoirs. He was not required to actually write anything himself, as the publisher provided him with a ghost writer. After six months, so the story goes, not a word had been written, and the publisher asked for the money back. The ghost writer was then allowed to interview Mick, but gave up. When asked about his early life, he allegedly said that it all started in the 1960s. “Keith said try a bit of this, and then I got out of the taxi this morning”.

  Following our discussion of radar and ASDIC, we will finish this section covering the struggle in the Atlantic convoy lanes by looking at the development of the U-boat during the 1940s. I believe that during the German arms buildup in the 1930s, one of Hitler’s major mistakes was to concentrate his resources in large single assets such as the Bismarck and Tirpitz. Admiral Karl Dönitz had argued repeatedly for an increase in the strength of his U-boat fleet.

  Many U-boats could be built for the same cost, in terms of both money and resources, as the cost of building a single huge battleship. Also, a single U-boat with a fifty-man crew is capable of destroying a battleship with a crew of 2,000 or more, as the Royal Navy discovered early in World War II in Scapa Flow. Had Hitler listened to Dönitz, the Battle of the Atlantic may have been very different. However, following the sinking of the Bismarck, Hitler realised that wolf packs were considerably more effective than a single battleship, and U-boat production increased at a great rate from this point onwards.

  Irrespective of how good your battleship is, and the Germans arguably had the best, they were still no match for the Royal Navy’s fleet. This was simply because they could be attacked by several Royal Navy battleships at the same time, splitting the firepower of the Nazi vessel and making its escape very unlikely.

  In addition, the Nazis had no aircraft carriers, and the ability of the Royal Navy to launch carrier-borne aircraft in the mid-Atlantic was a major factor in the sinking of the Bismarck.

  Although Dönitz eventually got his own way with new resources being poured into U-boat production, he also made some serious errors of judgement himself. Soon, his strengthened Atlantic U-boat fleet started to suffer increasing losses. This was primarily due to ASDIC, which he was aware of, but also to the centimetric radar fitted to the convoy escorts, which he was not aware of. When this CR was miniaturised and fitted to Allied aircraft, the U-boat losses mounted still further. Unknown to Dönitz and the Nazis, the British at Bletchley Park had also cracked the Enigma naval encryption code. The Germans blamed the increasing losses on the activities of spies.

  During World War II, U-boat warfare was the major component of the Battle of the Atlantic, which lasted the duration of the war. Germany had the largest submarine fleet in World War II, since the Treaty of Versailles had limited the surface navy of Germany to six battleships (of less than 10,000 tons each), six cruisers and twelve destroyers. Prime Minister Winston Churchill wrote “The only thing that really frightened me during the war was the U-boat peril.”

  In the early stages of the war, the U-boats were extremely effective in destroying Allied shipping, initially in the mid-Atlantic, where there was a large gap in air cover. There was an extensive trade in war supplies and food across the Atlantic, which was critical for Britain’s survival. Later, when the United States entered the war, the U-boats ranged from the Atlantic coast of the United States and Canada to the Gulf of Mexico, and from the Arctic to the west and southern African coasts and even as far east as Penang. The US military engaged in various tactics against German incursions in the Americas. These included military surveillance of foreign nations in Latin America and the Caribbean, in order to deter any local governments from supplying German U-boats.

  Because speed and range were severely limited underwater while running on battery power, U-boats were required to spend most of their time surfaced running on diesel engines, diving only when attacked or for rare daytime torpedo strikes. The more ship-like hull design reflects the fact that these were primarily surface vessels which had the ability to submerge when necessary. This contrasts with the cylindrical profile of modern nuclear submarines, which are more hydrodynamic underwater (where they spend the majority of their time) but less stable on the surface. Indeed, while U-boats were faster on the surface than submerged, the opposite is generally true of modern subs. The most common U-boat attack during the early years of the war was conducted on the surface and at night. This period, before the Allied forces developed truly effective antisubmarine w
arfare (ASW) tactics, was referred to by German submariners as “die glückliche Zeit” or “the happy time”.

  The U-boats’ main weapon was the torpedo, though mines and deck guns (while surfaced) were also used. By the end of the war, almost 3,000 Allied ships (175 warships and 2,823 merchant ships) had been sunk by U-boat torpedoes. Early German World War II torpedoes were straight runners, as opposed to the homing and pattern-running torpedoes which were fielded later in the war. They were fitted with one of two types of pistol trigger. The impact trigger detonated the warhead upon contact with a solid object, and the magnetic trigger detonated upon sensing a change in the magnetic field within a few meters.

  One of the most effective uses of magnetic triggers would be to set the torpedo’s depth to just beneath the keel of the target. The explosion under the target’s keel would create a shock wave, and the ship could break in two. In this way, even large or heavily armoured ships could be sunk or disabled with a single well-placed hit. In practice however, the depth-keeping equipment and magnetic and contact exploders were notoriously unreliable in the first eight months of the war. Torpedoes would often run at an improper depth, detonate prematurely or fail to explode altogether, sometimes bouncing harmlessly off the hull of the target ship.

  This was most evident in Operation Weserübung, the invasion of Norway, where various skilled U-boat commanders failed to inflict damage on British transports and warships because of faulty torpedoes. The faults were largely due to a lack of testing. The magnetic detonator was sensitive to mechanical oscillations during the torpedo run, especially at high latitudes, due to fluctuations in the Earth’s magnetic field. These were eventually phased out, and the depth-keeping problem was solved by early 1942.

  Later in the war, Germany developed an acoustic homing torpedo, the G7/T5. It was primarily designed to combat convoy escorts. The acoustic torpedo was designed to run straight to an arming distance of 400 meters and then turn toward the loudest noise detected. This sometimes ended up being the U-boat itself. At least two submarines may have been sunk by their own homing torpedoes. Additionally, it was found these torpedoes were only effective against ships moving at greater than 15 knots (28 km/h). Subsequently, the Allies countered acoustic torpedoes with noise-making decoys such as the Foxer, FXR, CAT and Fanfare. The Germans in turn countered this by introducing newer and upgraded versions of the acoustic torpedoes, like the late-war G7ES, and the T11 torpedo. However, the T11 did not see active service.