Early anti-

milestones MILE submarine STONES warfare Dr Carlo Kopp

The first conflict in which Anti Submarine Warfare became a priority was the Great War, between 1914 and 1918. The Kaiser’s fleet of U-boats was employed to great effect, interdicting British shipping lanes, as part of a broader attempt to blockade the British Isles and isolate Britain from its colonies, which provided both raw materials and troop reinforcements for the war effort on the continent. As the United States became progressively embroiled in the conflict, shipping lanes to the Americas became a target.

It is worth observing that the May 1915 sinking of the RMS Lusitania by U-20, with the loss of 1,200 lives, became a coup for pro- war campaigners in the United States and is often credited with being a key factor in the United States’ 1917 entry to the war aligned with the British. With the world’s largest fractional percentage of German immigrants and their descendants, the United States was under considerable domestic not to become involved. The scale of the Great War U-boat campaign may be modest by later standards, but it did set the path for much of naval warfare over the following nine decades and beyond. Cited statistics include 5,000 vessels sunk accounting for 12,000,000 tons of displacement, 15,000 people killed in U-boat attacks, with Germany deploying 372 U-boats, of which 178 were sunk, mostly by the . The enormous effort and marginal success rate against the U-boats produced enormous pressure to develop equipment to fight the U-boats, especially sensors, and this was the beginning of a continuous technological arms race which continues to this day. Two case studies are well worth closer study, which are and radar employed in early ASW operations.

Early Passive and Active Sonar Technology Sonar technology, which employs hydrophones to detect sound emissions from submarines, or sound much depended upon the talent and experience reflections off submarines, remains the mainstay Type IXC/40 boat U-185, under the command of of the operator, who effectively had to carry the KapitanLeutnant August Maus, sinking after being of ASW sensor technology employed to prosecute calibration information for the system in his head. depth charged by TBM Avengers of the USS Core on attacks on submerged submarines. In pursuit of a contact with turning screws, the RPM the 24th August, 1943. The U-185 was attempting The earliest and most common passive sonar to rescue the crew of the crippled U-604 but was provided an indication of the speed of the contact, installations used a pair of hydrophones under the found by US Navy aircraft and in two consective together with subtle Doppler shifts – most signals of the vessel, providing in effect a “stereo” engagements, damaged and then sunk. were in the hundreds of Hertz frequency range. acoustic signal to the hydrophone operator’s Typical pursuits involved having the operator call headset. The operator would use experience to out steering corrections and range estimates until estimate range by loudness, with the stereo effect the vessel was pointing at the contact, at which providing direction finding. Based mostly on period point a run could be performed. analogue telephone technology, such systems had An important advance later in the war was the poor sensitivity and direction finding accuracy, and DefenceToday - 33

DT_DEC2010.indd 33 14/12/10 4:59 PM introduction of steerable hydrophones, whereby The “Q” attachment produced a vertical fan shaped wing and nose mounted Yagi antennas and a a short horizontal boom with hydrophones was beam of around 65 x 5 degrees of arc, and was characteristic row of upper fuselage antennas. The mounted under the vessel, and remotely steerable designed to track a target in azimuth, but lacked first U-boat attack was effected in late 1940. The through a 360 degree arc. This allowed the operator a depth finding capability. It was range gated to ASV Mark II permitted daylight attacks on surfaced to perform bearing measurements without vessel 1,200 yards, and steerable through 360 degrees U-boats, while they recharged their batteries, heading changes. in azimuth, operating at 38.5 kiloHertz. The “Q” and while it could find U-boats at night it was This technology progressively evolved through beam could thus be employed to find the bearing not accurate enough to perform blind deliveries the 1930s and 1940s. Later designs employed of a target regardless of its depth. at night. arrays of up to two dozen piezo-electric crystal An additional capability integrated into this system The Kriegsmarine responded to the increasing loss or electro-dynamic moving coil hydrophones, and was the Type 147 “Sword”, which produced a fan rates in the U-boat fleet by installing the FuMB 1

milestones vacuum tube analogue electronics were employed shaped depth finding beam of similar geometry to Metox 600A, developed after a Coastal Command to perform angle measurement by comparing the “Q” beam. Wellington fell into German hands in Africa and its signals produced by each element. Additional This multiple beam arrangement allowed the use ASV Mark I was dissected. The Metox produced a hydrophones were employed as noise cancellers, of the relatively inaccurate but sensitive primary high false alarm rate, but even so, rapidly reversed feeding an out-of-phase copy of the ship’s own pencil beam to acquire a target at range, and as the losses in the U-boat fleet. noise output into the receivers to null out the ship’s escort closed on the target, the more precise fan The British response to the Metox was to deploy the own signature, which would otherwise drown out shaped beams could be employed to effect more 10 centimetre S-band ASV Mark III radar, initially a faint submarine signature. Submarines were exact angle measurements to determine bearing fitted to Coastal Command Wellingtons, using a also equipped with much the same technology, to and depth. nose mounted steerable paraboloid antenna. In evade other submarines, evade escorts, and hunt Contemporary active sonar arrays employ fixed early to mid 1943, a small number of ASV Mark III for targets. rather than mechanically steered tranducers, aircraft flew ASW patrols in the Bay of Biscay, and The technology of active sonar, or ASDIC (Anti- employ phased array techniques to form transmit since the Metox was blind in the S-band, achieved submarine Detection Investigation Committee) and receive beams in arbitrary directions within the a high success rate. An impulsive directive for in period British nomenclature, lagged behind angular coverage of the array. U-boats to engage the Coastal Command aircraft passive detection technologies, as it was more ASDIC and its American siblings proved to be a using their deck guns resulted in the loss of 56 technologically challenging. An active sonar critical technology in ASW operations, and remain U-boats in just over two months. needed to transmit, in a controlled fashion, a so today. While the Kriegsmarine developed and deployed pulsed sound signal which would propagate the S-band FuG 350 Naxos I warning receiver outward until it bounced off another object be it Early Anti-Submarine Warfare Radar to defeat the ASV Mark III, the British deployed a target or a seabed, or a “biologic” as in school Technology the S-band ASV Mark VI with selectable power of fish, cetacean or other organism. While some Surface search radar was the “other” pivotal settings intended to deceive the U-boat operators viable trials and experiments were performed late technology which won the Battle of the Atlantic. by reducing power to suggest the aircraft had not in the war, ASDIC did not become an operational Its development followed a far more tortuous acquired the target. capability until the interwar period. path than ASDIC/Sonar systems, since radars The next step in this cycle of measures and By the time the Battle of the Atlantic was in full for maritime search purposes directly competed counter-measures was the introduction of the ASV swing, ASDIC systems were widely deployed on for development and production resources with Mark VII, operating at 3 centimetres in the X-band. Royal Navy and other Commonwealth navy escorts. radars intended for night fighters, and later heavy The Mark VII was based on the technology in the A good example of a period system was the ASDIC bombers. The result of this competition was that H2S blind bombing radar, carried by Royal Air 144Q system, operationally deployed in 1943. The programs were started and stopped, as short heavy bombers. transducer array was installed in a streamlined term priorities and bureaucratic politics caused By late 1944 the Kriegsmarine’s U-boat effort pod under the hull of the warship, and was resources to be shuffled. began to collapse, as Allied ground overran steerable in azimuth. The primary sensor produced The first maritime search radar to be built in ports along the Atlantic coast. Around one half a conical 16 degree “pencil beam” which was useful numbers was the ASV Mark II, which was of the U-boat fleet at that stage were fitted with steerable in azimuth, and range gated for 1,000 carried on a wide range of maritime aircraft, snorkels, which effectively defeated the ASV Mark and 2,500 yards. It transmitted pulses at nine including the Sunderland and Catalina flying boats, III and VI radars. selectable acoustic carrier frequencies between 14 and maritime variants of the Whitley, Wellington, The Americans suffered heavy losses to coastal and 22 kiloHertz, in 1 kiloHertz increments. Two Warwick, Halifax and Liberator, all converted from shipping by U-boat attacks and deployed a large additional sonar transceivers were integrated into bomber variants. number of patrol aircraft as a result, operated by this system. This ungainly 1.7 metre VHF-band design employed the Army Air Corps and Navy. The first ASW radar deployed was the 10 centimetre S-band SCR-517, derived from the SCR-520 air intercept radar, and fitted to modified Army Air Corps B-24 patrol bombers from early 1942. These were also supplied to the Royal Air Force as the ASV Mark V radar. The US Navy deployed a large number of ASG or AN/APS-2 10 centimetre S-band search radars on maritime patrol aircraft, including the PBY Catalina, PBM Mariner, PV-1 Ventura and PB4Y-2 Privateer – in converted bombers the APS-2 antenna was usually lowered through a ventral turret well, or faired into the nose. These aircraft were used to fight U-boats along the Atlantic coastline, and Japanese submarines across the Pacific theatre.

ASDIC equipped escorts were a critical component of the Allied convoy effort. Depicted is HMS Charybdis which was sunk by a U-boat torpedo.

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DT_DEC2010.indd 34 14/12/10 4:59 PM An early model Coastal Command Liberator Mk.II based on the B-24D, equipped with the British four gun dorsal turret, and a US built SCR-517 ASV Mark V S-band radar system under a large chin radome. This aircraft operated by RAF 120 SQN survived the war, only to be destroyed in a landing accident.

analogue electronics to modern high performance A Perspective on Early ASW Technique to fly to maximise the odds of catching a U-boat. Because the Battle of the Atlantic is so well digital systems. In perspective, the technological battle between documented, it is very easy to observe the cyclic With the currently growing proliferation of modern the Allies and Kriegsmarine was unprecedented pattern of shipping losses and U-boat losses, and very quiet submarines globally, and some in breadth and depth, and displayed a rate of as each side deployed new technology or very potent and technologically advanced anti- evolution not seen until the electronic battles over technique, and the other side adapted by deploying shipping weapons intended to arm them available, Vietnam two decades later. a countermeasure or changing technology and there are good strategic reasons to recapitalise As in many other areas of military technology, technique. ASW fleets and do so very thoroughly. No less much of what transpired during the subsequent It would be reasonable to describe the 1940s as a importantly, serious thinking in technological Cold War period amounted to the exploitation of “revolutionary” period in submarine warfare and strategy is required, since we are beginning to 1940s technology, and its further evolution and ASW, while the Cold War was an “evolutionary” observe creative and independent technological refinement. period, and the post Cold War era a “stagnant” evolution in nations which were not part of the A contemporary sonar, maritime radar, radar period. There has been very little substantial technological arms races of World War II and the warning receiver, sonobuoy, magnetic anomaly technological evolution in submarine technology Cold War. Not to do so could see unpleasant future detector, or diesel exhaust detector will be or ASW since the end of the Cold War, with the surprises no different to those which confronted immeasurably more capable and technologically most important advances being incremental, and the Allies when the Battle of the Atlantic started sophisticated in comparison with its 1940s era mostly related to the movement away from legacy seven decades ago. ancestor. Yet what it is, and how it is employed, differs little in fundamentals from what was devised seventy years ago. Much less appreciated is that the Battle of the Atlantic involved the first large scale use of operational analysis techniques, where the Allies recruited a respectable number of mathematicians and other scientists to analyse and study operational effectiveness of various systems, but also operational technique, such as what were the best search patterns for a maritime patrol aircraft

Type XB boat U-118 under attack by US Navy TBM Avenger aircraft near the Canary Islands, 12th June, 1943. It sank with 43 crew killed.

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