ASDIC/SONAR GENERAL INFORMATION
The first device used to locate submarines is called Asdic (named after the Anti-Submarine Detection Investigation Committee) and was invented during World War I by British, American, and French scientists. This system located underwater objects by transmitting an acoustical pulse of energy, then listening for any echoes returned from that object. From ASDIC, the more modern term SONAR was borne, which means SOund NAvigation and Ranging. SONAR is an American term dating from World War II and is now used universally to describe all underwater detection equipment. In the RCN, the term SONAR started coming into general useage around 1955 and in the Royal Navy, around 1964.
There is also a considerable amount of confusion about the origins of the term 'ASDIC'. To quote Willem Hackmann from Seek and Strike, "The Oxford University Press was prompted on 11 December 1939 to ask the Admiralty about its etymology after Churchill used the term in the House of Commons. After a certain amount of inter-departmental discussion, they were told that the word was the acronym of Allied Submarine Detection Investigation Committee. This body was formed during the war of 1914-1918, and organized much research and experimentation for the detection of submarines, however, no committee bearing this name has been found in the Admiralty archives."
This newspaper article titled "Inventor of Sonar Ignored By History" was written by Geoff McMaster of the Express News Staff and gives some insight about the invention of ASDIC/SONAR."February 15, 2008 - Edmonton -- Robert Boyle could hardly have foreseen that he would come up with the most important military innovation of the First World War. And yet his story becomes, in the words of historian Rod McLeod, one of the most "fascinating and completely neglected" in the history annals of the University of Alberta, Canada.
Boyle was trained in the fledgling field of radioactivity and earned McGill University's (Montreal) first doctorate in science under Ernest Rutherford. But when he was recruited by the University U of Alberta founding president Henry Marshall Tory in 1912 to run the physics department, Boyle found the university ill-equipped for his primary area of research and turned his attention to acoustics.
Then war broke out. The Germans were using submarines as weapons, and the allied forces were desperately searching for ways to detect them. "Everybody starts working on this because the German submarines are sinking hundreds of allied ships," said McLeod. "The French are working on it, the Brits are working on it and the Americans are working on it."
The British admiralty set up a Board of Inventions and Research (BIR) in the hopes of putting a speedy end to the war. Rutherford was on the BIR panel and asked his former PhD student to join the research team in England, which was investigating a variety of potential detection methods. "He's put in charge of what they think is the least promising (line of inquiry)," said McLeod, author of the forthcoming book, All True Things: A History of the University of Alberta, 1908 - 2008.
Exploring the use of sound to detect objects underwater was a hot topic, at least since the sinking of the Titanic in 1912. A number of researchers, including the French physicist Paul Langevin, had worked out the theoretical principles for sonar, but getting a detection device to actually work on a warship proved daunting. Working closely with Langevin, Boyle and his group managed to produce working ultrasonic quartz transducers by 1917. These were installed on warships just a few months before the end of the war. "It turns out Boyle is the one who actually comes up with the first working model of sonar, beating out the other groups," said McLeod.
The innovation didn't come soon enough to make a difference in that conflict, but it laid the foundation for sonar detection in the years to come. As great as the discovery was, however, and perhaps partly because it was shrouded in secrecy at the time, Boyle "received no credit for his work even within his own university," writes McLeod. "Robert Boyle has at least as good a claim as any other individual to be the inventor of sonar. He took out no patents, as Langevin did, and because of the secrecy imposed on the invention by the Royal Navy in the 1920s, he published no papers on it."
And yet, "it had a greater impact on the subsequent military history of the 20th century than any other piece of military/scientific research carried out by either side during that conflict," writes Macleod. "It stands out as the most important new piece of military equipment developed by any Canadian scientist during the First World War."
Boyle was not to be seduced by a career in the military, however. He turned down an offer from the British Admiralty to work for twice his U of A salary and ended up back at the university, where two years later he became dean of the newly established Faculty of Applied Science".
|HMS P59 received the world's first ASDIC set in 1919. This is a post card from C.&S. Kestin, Weymouth, England. (No copyright claimed on post card. Submitted by Øyvind Garvik)|
The first reference to ASDICS occurs in the weekly report of experimental work at Parkeston Quay, Harwich, dated 6 July 1918. This word replaces the section heading of supersonics, dealing with these experiments. After this date, the new term appears very frequently in the records. No indication is given for this sudden change of term. It almost certainly stood for 'pertaining to the Anti-Submarine Division'(or Anti-Submarine Division-ics), the Admiralty department that had initiated this research.
During the later part of World War I, submarine locators were developed. These devices were frequency sound receivers (also known as hydrophones) and were designed to receive low frequency sound because this type of sound travels farther in water than high frequency sound. Success in detection was dependent on the noise level of the target and the Germans soon learned to rig for silent running. These primitive sets could only measure target bearing, therefore, the submarine had a good chance of escaping.
Asdic operated by transmitting regular pulses of sound energy that travelled through the water and were reflected by a target. This energy resembled the beam of a searchlight and was projected horizontally. Any resultant echo was received, amplified, and then displayed on a recorder. The time that elapsed between transmission and reception indicated the distance from the Asdic set the target. A display mechanism, which had a time base, transformed the echoes into electrical impulses that normally caused a stylus to mark a strip of paper moving on rollers. Together with bearing and depth information, the location of an underwater target could be pinpointed.
Just like radar, the resolution of Asdic improves as the transmitted pulse is made shorter. If the sound beam is narrowed, the capability for distinguishing two targets at different angles improves. This is known as angular resolution. Range and effectiveness of Asdic are affected by many factors. The water surface and sea bottom are natural limits to the propagation of sound. In some cases, layers of water can stratify at different temperatures. This temperature inversion can cause the acoustic beam to be deflected toward the bottom, where it will be reflected upward to the surface, down again, and so on, rendering the Asdic useless. Sound travels around 4,800 feet per second in 40°F sea water as compared to 1,100 feet per second in 40°F air.
Ian Snow, RCAF Ret'd., expands on this. "There are three major factors that affect the propagation of sound in water. Temperature has the greatest effect, especially in the upper layers (where the diesel boats operate). There is a very shallow layer, measured in feet, which will change with the daily sun cycle. Below than is an intermediary layer whose depth is "somewhat" more stable and changes with the time of year and the degree to which storms have caused the water to mix. Below that point, pressure becomes the dominant factor and increased pressure will cause sound to refract (vice reflect from the ocean surface or a distinct temperature boundary). This can create deep sound channels that conduct sound for thousands of miles depending on frequency, channel depth, etc. etc. This is exploited by the shore-based and towed array. Pressure will also refract the sound energy back up to the surface, where it can pass through a very narrow band (convergence zone) between the surface and (say) 100 feet where the temperature profile again bends the wave back down. This can happen several times creating a number of "donut" convergence zones. Salinity is the third factor but has the least effect generally speaking. In the Atlantic Ocean for example the distance from source to the beginning of the first convergence zone (CZ) is on the order of 32 nautical miles. In the eastern basin of the Mediterranean where salinity is very high the CZ distance can be as little as 15-16 nm. The Strait of Gibraltar is a very difficult area to detect a submarine because the warmer westbound Med water, more dense because of the salinity, is flowing out into the Atlantic under the colder less dense Atlantic water which is flowing eastbound. The subs would strive for neutral buoyancy in the flow and drift through the straits in silent mode to evade detection by the (reportedly) fixed acoustic surveillance arrays.
Turbulent areas of water may scatter the beam, causing the signal strength to fluctuate and distorting the reflections. The water may also absorb the sound energy, transforming it into heat; this heating effect increases rapidly as the transmitting frequency is increased. The velocity of the sound wave and hence the accuracy of distance measurement is affected by the temperature, depth pressure, and salinity of the water. Sound velocity rises in direct proportion with these parameters. Acoustic noise limits the range of Asdic, because it masks the reflected signal. Such noise may be caused by wave action, aquatic animals, or other surface craft. The speed of the ship is also a limiting factor as the water passing by the Asdic dome creates its own sound energy and can hide any weak echoes.
A problem with early Asdic's was their limited search ability as the oscillator projected its cone shaped beam at an angle of 10 degrees from the horizontal. Below the beam of acoustical energy was a considerable amount of dead space that would permit the target to elude Asdic. If the enemy escaped detection, depth charges had to be dropped by estimating the target's position. Wartime experience showed that this dead zone was even larger than envisioned because submarines could dive far deeper than was originally thought possible. As a result, a clever submarine commander could often manoeuvre out of harm's way. Once contact was lost, it was very difficult to re-establish.
When operating in conjunction with other detection ships, it was very important that all the operating Asdic's were tuned to different frequencies. If an operator was negligent of this, a transmitted pulse from another ship's Asdic would be detected as an extremely loud echo on another set. The operators' ears would experience the threshold of pain as the amplified echo thundered in his headphones. The Asdics developed during the war operated on a number of discrete frequencies between 14 and 22 Kcs. Power output of oscillators was inversely proportional to the operating frequency. Many operators favoured operation in the 14 to 15 Kcs range because they believed that greater ranges could be obtained as contrasted by operating at 18 to 20 Kcs. It was well known that greater ranges could be had at 10 or 12 Kcs, but that meant increasing the oscillator size. It was a trade off.
Asdic set designs generally fell into one of two categories depending on the type of Asdic dome. In the first type, the oscillator was housed in a dome fixed to the bottom of a vessel near the bow. The second type was housed in a retractable dome that could be positioned inside a chamber built into the hull of a vessel. Normally, this last type was fitted into vessels whose operations could damage an unretracted housing. Destroyers, which could damage their domes while operating at high speeds, and minesweepers, which could foul Asdic domes with their sweeping gear, were typically fitted with a retractable dome. To protect Asdic sets from ice damage, the RCN decided to fit all new vessels with retractable domes in mid-1942. When the dome was in the housed position, it precluded using Asdic. Corvettes, Fairmiles and converted yachts that only incorporated the most basic of necessities, did not have retractable domes.As a result, many of these ships sheared their domes by striking logs or chunks of ice off the coast of Newfoundland. These fixed installations were not very successful but it was better than not having any system. When corvettes discovered a U-boat lurking in the depths, it became practice for the corvette to try to drive the U-boat underwater where it was slow and nearly blind, then return to the convoy. Trying to overtake the U-boat was pointless since the surface speed of the U-boat was slightly higher than that of a corvette. Later on, design improvements produced a sword shaped oscillator whose physical appearance resembled that of a sword and the angle from the sword to the bow could be altered to detect deep targets. In some Fairmiles, the oscillator was fixed to the hull and to train it on a new bearing, the ship would have to be turned. The standard procedure was to steer on the contact while altering course in a cast off fashion and back on again until the ship was able to drop depth charges.
From its inception in 1917 until the late 1940's, the detection range of Asdic remained at basically 2000 yards. True, during World War II, there were refinements in fire control and depth measurement, but the range remained much the same. If conditions were ideal, a target at a range of 3000 to 4000 yards could be detected and but that was the absolute limit. Contrast this to today's hydrophone technology that can detect the propeller noise of a diesel electric submarine at distances of 100 nm. A modern system can also identify the class of submarine by comparing the hydrophone signal to a pre-loaded signature in the memory of a computer. Tactically, an Asdic that only produced a narrow beam was very useful for attack, but not for search, since it could not look rapidly in many directions. It was not until the end of World War II that 'true' search sonar was introduced into the world's navies.
Frank Curry, author of the book War at Sea, does an excellent job in depicting the challenges of making it from a raw recruit to a submarine detector. Here is an excerpt from his book: "The Asdic training program covered little about U-boat warfare, strategy, tactics or philosophy. From the day we signed the document committing ourselves to Asdic for the duration of the war, I cannot recall a single lecture or paper about the war at sea and our part in it. We were left entirely out of the big picture, except merely to absorb training and carry out duties to the best of our abilities.
The training to convert us into submarine detectors (SD) was intensive, beginning with a thorough run-through of the theory of Asdic, and the equipment developed to apply the theory. The earliest equipment consisted of a large, flat, round transmitter that would be lowered or raised inside a dome fastened to the keel of the ship. The dome was usually positioned directly under the bridge. In a compartment surrounding the transmitter and dome, the transmission equipment, powered by high-speed motors, created the sound beam, sent it out through the transmitter.
The submarine detector's job was to control the transmissions sent out every few seconds on a sweeping arc. We were taught to use earphones to follow the sound of the transmission out to its limits, 3000 to 4000 yards under ideal conditions and to listen intently for any sign of an echo. An echo was the ultimate sound of danger; the trigger for action stations; the start of attack procedures leading to the firing and dropping of 150 pound depth charges in patterns aimed at the conning tower of the attacker. Along with echoes, we were expected to listen for any sound of engines or motors in the ocean's depths.
We spent weeks getting used to the equipment and then faced what would be the bane of every SD in the navy -- the attack table, a sophisticated and monstrous mock-up of a convoy operation, including escort ships, columns of merchant ships and attacking U- boats plus a variety of weather conditions and water vibrations. These were staffed by a veteran group of Asdic staff members including Commander Welland, the top anti-submarine expert in the Royal Canadian Navy.
They drove us young and inexperienced recruits to the breaking point. Commander Welland created impossible situations; wreaked havoc; drove us to tears by screaming and yelling at our mistakes and breakdowns. He seemed determined to come as close as possible to the combat situations we would all face when isolated aboard a destroyer, a corvette or a bangor. It was a fearful and soul destroying introduction to the war at sea before we ever put a foot aboard an operational ship. For the rest of the war, in whatever naval port we found ourselves, all the Asdic's spent every hour in an attack-table bus, hammered and harassed with every new element of Asdic operations. We spent week after week in the Asdic school, and many of us felt we were caught up in an impossible situation. There was no backing out; we were in it for better of for worse.
Finally came the day when we took our classroom knowledge to sea. Off we set for St. Margarets Bay, down the coast from Halifax, and aboard an Asdic equipped training ship. In the vast peace and calm of this magnificent bay, we joined a Dutch submarine for ten solid days and nights against a German U-boat -- simulated by our Dutch ally. It dodged and wheeled in the depths, shutting off its engines and sitting silently, on the bottom as our Asdic transmissions tried to establish contact.
Contact was made...the attack began...the charges were dropped...contact had to be maintained...contact was lost. We were subjected to a scathing criticism by Commander Welland as we continuously blundered our way through the procedure. Finally, a brief word of praise for a correct manoeuvre." These SD ratings knew that the lives of their fellow shipmates and those on other ships in the convoy rested on their ability to detect a submarine. It must have been a big burden to carry!
Operating the Asdic required undivided attention. After a two hour watch, operators were generally happy to see their relief show up. It became so monotonous listening to the pinging, that many S.D.'s even heard those transmissions in their sleep. After several weeks at sea, the Asdic crew was completely drained from this and never received a decent rest. Duty watches varied by ship. Sometimes it was two hours on and two hours off. Other schedules called for four hours on and eight hours off. While on duty, one operator would spend one hour on the set and one hour on lookout then the procedure would be reversed. On some ships, the S. D's were relieved of other duties such as cleaning ship or swabbing decks. Asdic operators also acquired the nickname of 'ping merchants'.
John Coates of Tantallon, N.S. recollects the small anti- submarine school that was built at HMCS Stadacona, Halifax at the time Canada entered World War II. "It was a small building, just behind the gymnasium. All of the equipment came from the United Kingdom. LCdr A/S Robert 'Bob' White, RN was put on loan to the RCN as the Officer-in-Charge of the school. Soon, he was joined by Lt. A/S Robert 'Bob' Timbrell of the RCN who had just finished his A/S qualifications in the UK. LCdr White was an ideal choice for his posting as he was very decisive but kind in his tone of voice. The were no scathing or superior remarks from him, but you knew that he was qualified.
These two officers soon set up the courses for submarine detection (SD) and higher submarine detection (HSD). Very quickly, the school was full and we were put through our paces. The very first Asdic ratings were being turned out in Canada. The courses concentrated on equipment maintenance and the detection and destruction of submarines. The broader aspects of anti-submarine warfare were none of our concern.
I am not sure how long LCdr White stayed in Canada, but when I qualified as an SD he was certainly running the show. Later, he turned over control to Cdr Robert 'Bob' Welland, RCN. It seems that the first people are named Bob. When HMCS Cornwallis was being planned, it was determined that an Asdic School would be built there. The old school would be retained for Asdic teams from ships in harbour to have a 'brush up' under the eyes of a small training staff. Later, as the Group Anti-Submarine Officer serving in HMCS Digby, I took the various teams from the ships in our group to the original facility for refresher training".
Wilf Knecht of Nanaimo, British Columbia was a former Asdic rating and he provides an impression of Asdic operations aboard HMCS Haida during the 1944/45 period."A normal duty watch consisted of two operators manning the equipment. The Asdic recorders were located in a cabin below the bridge, on the port side and off the plot room. Under normal conditions, one rating operated the Asdic and communicated with the bridge using voice pipe while the other stood by. Both operators took turns in the active position.
When Action Stations were sounded, three operators sat on a bench in front of the Asdic and actively manned it. An HSD monitored the proceedings. On the left side of the bench, sat an operator who read out the bearing if a contact was acquired. Any rapid change or loss of bearing also had to be reported to the bridge. The centre operator operated the training control, raised and lowered the dome and controlled the firing of the depth charges. The right most rating would operate the range finder. A gyro compass repeater was provided for use by the middle operator and a magnetic compass was also fitted in case the gyro failed. When using a magnetic compass, a stop watch had to be used to establish range.
When leaving or entering harbour, the Captain or Officer of the Watch would inform the Asdic hut when to lower or raise the oscillator dome. It had to be raised if Haida was steaming above 20 knots or dome damage would result. Sometimes this was forgotten by the bridge and the Asdic operator would have to request permission to raise the dome. Operators did not search the sea at random. The normal search procedure in most cases was given as: set range to 2000 yards and begin search from Red 30 degrees to 5 degrees past the bow. If no echo was returned on the given bearing, the operator would search from Green 30 degrees to 5 degrees past the bow. This sweep was repeated until ordered otherwise or a contact was made. If a contact was made, the range recorder operator would reduce the automatic transmission time to eliminate the lag time between transmissions as the target drew closer to the attacking vessel.
Every contact had to be classified for type, distance, direction and be reported to the bridge immediately. Operators had to be aware of the Doppler effect, which is a change in pitch of the echo as the target moved closer or more distant. The operator had also had a chance to demonstrate his skills in determining if an object was a whale, tide or water conditions, large schools of fish, rock formations or old wrecks." One point that Wilf highlights is the fact that there was no documentation issued to Asdic ratings due to the prevailing level of secrecy. Jim Fairnie of Victoria B.C. recalled another side to this secrecy. "Asdic operators were prohibited from wearing Asdic badges on uniforms while at sea in case their vessel was torpedoed and they were picked up by the enemy. To add to the disguise, the operators wore a torpedoman's badge."
Because Asdic transmissions were audible by their nature, operators had to wear headphones to hear the incoming echoes. Since it was also necessary to communicate with the bridge, the operator could not keep both ears covered so the one earpiece was placed against the side of the head and then switched occasionally. If a contact was acquired during Action Stations, its echo could be patched into the ships loud hail to keep everyone informed as to status. When not operating Asdic, operators would be assigned to the plotting table or the depth sounder."
John Coates explains his role in Haida's Asdic room. "In action, I took up my station behind the operators and wore my chest set. This was merely a set of headphones and a chest microphone. One earpiece was wired to monitor the contact and the other was connected to the bridge/ops room circuit along with the microphone. There was an extra long lead on the headset so I could step around the corner and see the Plot.
If I wanted the most current contact status from any of the operators, I would touch them on the shoulder as part of an established drill. We did keep a continuous flow of bearing and range information to the bridge and the Plot and consciously kept the verbal chatter to a minimum.
Rear Admiral Bob Welland (Ret'd) of Ottawa Ontario, relates some of his wartime experiences as CO of Haida and Assiniboine. "The CO's of the ships in a squadron or group got to know each other well and usually had opportunities to discuss the last operation and the up and coming one. We also compared our habits at sea. For instance, I stayed up at night because that's when the action happened and I knew that the Officers of the Watch could handle the situation in daylight. Also, I never got undressed except to wash up. I arranged an Asdic gyro indicator to be fitted in my sea cabin along with a speaker that pinged if an echo was detected. Upon hearing an echo, I would wake up and using the voice pipe, I would have the ship turning before making it up the ladder to the bridge. I was not alone in this. Many of the senior operators and the HSD's slept in the Asdic office for the same reasons.
Over time, it got to the point where the CO's of various ships created a 'pool' and took bets as to which ship would be torpedoed or be in collision. I won twice but had to share the pot with another Captain."
Harry Carson, Ex-C.P.O. 1st Class of Dartmouth N.S. relates some interesting details on how to remove an Asdic dome without availability of drydock facilities."Londonderry was our home port on the other side. To get into this port, we had to travel up the River Foyle. This river was narrow and very shallow and our corvette could not navigate upriver without removing the Asdic dome. The procedure for doing this was out of this world.
First, you had to perform a watertight test to ensure that the cover plate at the top of the dome trunk was not leaking. The forward and after lifting screws would have to be slackened off in order to crack the seal between the dome and the trunk. If there was no indication of a leak, the lifting wires of the dome would be slackened until the dome was hanging on stainless steel cables, about two feet clear of the keel. A long heaving line would then be brought up to the bow and its centre was marked with a piece of coloured bunting.
The centre of the cable was placed over the bow of the ship and the free ends were positioned on the port and starboard sides. As you walked aft on either side and payed out the cable, you could feel the line dragging on the centre line of the bottom of the hull. When pressure on the dome lifting wires was observed or if the line snagged, this was an indication that contact has been made with the dome. One end of the line would be secured and the opposite end would be dragged aft and secured to the upper deck just ahead of the propeller. A large bight (loop) of cable would then be laid on the river bottom and the excess would be passed under the propeller while walking forward with the cable and maintaining the bight. When the cable fouled the dome lifting cables, it was secured to the upper deck again and the slack would be taken in. With any luck, both lifting cables would break the surface.
After the dome broke surface, a sailor in a Bos'n chair would secure a winch cable in the afterlifting eye bolt in the opening of the dome. A three inch suction hose was then placed in the dome and the water was pumped out until the transducer shaft spindle was exposed. After the spindle was removed, the remaining water was pumped out and the dome was winched inboard. It was very important to ensure that the dome was nearly free of water before being hoisted, otherwise, the weight of excessive water might rupture the Staybrite steel skin of the dome. Once the dome was secure, the ship continued upriver to Londonderry. To add interest, the River Foyle presented two 90 degree bends which made the task of navigation somewhat interesting. On leaving port, we used a lead line to take soundings. When we determined that there was sufficient clearance between the hull and the river bed, anchor would be dropped and the dome would have to be re-installed. The fun would begin again."
Maintenance of Asdics and especially oscillators was a thorny issue. During the war, it was policy to limit the knowledge of the operators and officers for security reasons. In-depth knowledge of Asdic was limited, so very few personnel could tackle the task of repairing a defective oscillator or an Asdic while the ship was at sea. It was forbidden to take an oscillator apart, yet it was the only way in which many a broken set could be made functional. In retrospect, there were many Jack-stay transfers to enable precious few people to repair an inoperative Asdic. The reason for this policy lay in the secrecy surrounding the design of the piezo quartz strips. The quartz was mined in Madagascar and secreted to the United Kingdom and Canada. In Canada, the quartz cutting was done in a lab on Sussex Drive in Ottawa. Machining had to be very precise. For example, if a 15 Kcs oscillator was 'off tune' by even 300 cycles, its performance dropped dramatically. In retrospect, the secrecy worked as the Germans never caught on to the technology during the war. In the inter-war years, this subject was considered to be so secret, that no reference to quartz was permitted. Instead, quartz in the context of Asdic was referred to as 'asdivite'.
Rear-Admiral Bob Welland (Ret'd) relates his WWII experiences when replacing a defective oscillator at sea. "While serving in Corvettes, I personally changed several oscillators in mid-Atlantic which had broken down. Oscillator replacement was not permitted at sea unless an expert was doing it - someone who knew the risks. When the top of the mechanism was unbolted to lift out the oscillator (on the end of a 6 foot shaft) there was a hole in the ship 3 feet wide and only the skin of the dome was holding out the ocean. This hole was about 7 feet below the waterline! When it came time to do the job, we locked ourselves in the compartment, closed all apertures and trusted that the skin held. It always leaked slightly in order to keep the dome flooded. Usually it took about an hour to replace a 400 pound oscillator. In some Corvettes, there was an air pump fitted to pressurize the compartment while the top was off the mechanism but usually it was not serviceable!"
Contributors and Credits:
1) Ian Snow <va3qt-4(at)sympatico.ca>
2) Øyvind Garvik [email@example.com]
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