RN Subs

The History Of British Submarine Sonars

by Commander David Parry

The Early Years

The Fessenden oscillator is adopted and modified

Titanic. The name of this famous ship (or infamous, depending on the way you look at history) reverberates throughout the century since she sank in 1912. Her sinking was the instigator of many changes, developments and innovations not least the genesis of the US Coast Guard and SOLAS.¹ Among the innovations of how to detect obstructions at sea, like an iceberg, was one conceived by a Canadian born radio engineer, Reginald Fessenden working as a consultant to the Submarine Signal Company to enhance their system of underwater bells for shore-based stations, buoys, and light ships and for sound detection on ships.² It may well be that the Royal Navy had experimented with these underwater navigation aids for BR 3043 reports "a report dated 9 February 1909 stated that 'submarine sound signalling had been fitted in certain submarines and tests carried out with bells fitted on the Shambles and Tongue Light Vessels'."³ Fessenden's invention was an electro-mechanical oscillator, in effect a transducer,⁴ transmitting sound through the water at 540 Hz. He patented the oscillator in 1913 and trials of the system were an outstanding success.⁵

The Royal Navy was immediately interested and submarines began to be fitted with Fessenden hydrophones.⁶ But the Fessenden hydrophones were cumbersome, weighing 559 kg,⁷ so the Torpedo School was charged with developing them for submarine underwater signalling (in 1917 the work transferred to the Signal School).⁸ The work was started under the redoubtable Commander (later acting Captain) CP Ryan at HMS Tarlair, the Hawkcraig Admiralty Experimental Station, Aberdour. Ryan was very much an old-school retired Commander re-called to service and then promoted. He was not a scientist, and he knew little or nothing about sound theory or instrument design. Yet, with an enthusiastic if eclectic staff that included a totally blind man with 'absolute pitch', the elderly son of a celebrated historian, a famous violinist, a London theatre manager and two eccentric dogs.⁹ Nonetheless he had managed to get a variation of the Fessenden system to sea with trials in the submarine B3.¹⁰ (Another product of Ryan's work was a "much more sophisticated arrangement of five powerful and sensitive hydrophones by which they could approach an enemy and obtain her position without using the periscope.")¹¹ These arrays went into the R Class anti-submarine submarines of which 10 were completed just before or just after the end of WW1 but only two survived beyond 1923. However, they were not used to develop tactics for their intended role and the potential of the array was not explored. Later, the Germans used hydrophone arrays extensively; the Royal Navy not until asdic Type 186 in the 1950s.¹²

Ryan's work resulted in two new designs: an improved Fessenden which became Type 102; and a transmitting-only version that was designed to talk to submarines under tow. WW1 submarines, including the E Class and L Class, were fitted out with the Type 102 but research continued with upgrades until 1931 when the S Class were fitted with Type 106X¹³ operating at 1080 Hz.¹⁴

Early outfits had two 5 inch plate hydrophones of a new design (either a Mark II, IV or V) and tuned to 900 Hz that were fitted in the submarine's pressure hull, both forward with one on either side.¹⁵ By 1926, a third plate had been added, facing aft, "immediately abaft, or inside the after superstructure of the conning tower; it should, when possible, be placed not less than five feet above the pressure hull." ¹⁶

There were three principles behind the installation of this apparatus: safety, attack and navigation or tactical. For safety, it was considered possible to detect another dived submarine and so avoid collision. The attack mode was severely limited, and the submarine had to be swung across the bearing of the target to find the null point between the two forward hydrophones. Unsurprisingly, this was not considered to be very successful¹⁷ so the deficiency was rectified by the later installation of the Revolving Directional Hydrophones (RDH). The navigational use was for the detection of the submarine bells and the tactical was the start of sound telegraphy (S/T sometimes later called S.S/T or SST)¹⁸ whereby a submarine could both listen to the message and get a bearing on the transmitting submarine. The thought was that this would allow submarines to operate together in, for example, a patrol line.

Ranges out to 20 miles for SST were claimed but reception could be seriously affected by ambient or own ship's noise.¹⁹ The advice was for the operator to listen on all three hydrophones at the same time especially if SST was expected and some of the principles for a passive search housekeeping that would last well into the future were laid down. For example: slow speed to reduce flow noise; casing rattles had to be eliminated; machinery to be stopped (apparently the hydraulic system particularly interfered); and the operator was to be informed of course and speed changes and pump starts/stops etc.

In submarines, the Telegraphists were used to operate SST and the hydrophones and had the post-nominal HL, for Hydrophone Listener. There were two reasons to use the telegraphists: the transmissions used Morse code (the Morse for the letter 'F' was used for ranging) and the W/T amplifier was used to amplify the hydrophones signal. This meant that the hydrophone switchboard was co-located with the W/T amplifier although a pair of headphones was provided in the control room for the captain and later an extension listening station was in the fore ends to keep the operator away from the machinery noises²⁰ but it was a monotonous work resulting in operator fatigue and the necessity for frequent changes of operator.²¹ Submarines, of course, did not have large complements — the H32 had 42 crew members — so telegraphists probably found themselves watch and watch about. In 1920, such was the enthusiasm for asdics, that the General Service SD (Submarine Detector) branch was established being formed by selected seamen ratings under the age of 25.²² In submarines the job was still done by Telegraphists, called Telegraphist Detectors, and trained as asdic operators at HMS Osprey in Portland²³ which had been established as the antisubmarine school in 1924. But as late as 1937 sufficient numbers of suitable telegraphists could not be found; although it was hoped to resolve the situation by 1939!²⁴ The branches stayed like this until 1947 when both surface ship and submarine asdic operators became members of the Underwater Control (UC) branch.²⁵

The Revolving Directional Hydrophone

Towards the end of the war submarines began to be fitted with a set of revolving hydrophones positioned outside the hull. Initially this was supposed to be in the stem of the boat as shown, see Figure 1,²⁶ but this was amended to be on top of the forward casing as appears in Figure 2.²⁷ The apparatus consisted of two plate receivers, back to back, and connected by a rod. When either of the plates was pointing directly at the sound source there would be maximum movement on the rod and therefore maximum reception. Conversely, when both hydrophones were receiving the same amount of noise they would cancel each other out resulting in no rod movement and no reception. This was known as the 'minimum property' and was estimated to provide a bearing with an accuracy of ± 10°²⁸. The plate hydrophones were more sensitive and could detect sounds to three times the range of the RDH hydrophones. Even so, the RDH had detected surface ships up to nine miles.

The Royal Navy was immediately interested and submarines began to be fitted with Fessenden hydrophones.²⁹ But the Fessenden hydrophones were cumbersome, weighing 559 kg,³⁰ so the Torpedo School was charged with developing them for submarine underwater signalling (in 1917 the work transferred to the Signal School).³¹ The work was started under the redoubtable Commander (later acting Captain) CP Ryan at HMS Tarlair, the Hawkcraig Admiralty Experimental Station, Aberdour. Ryan was very much an old-school retired Commander re-called to service and then promoted. He was not a scientist, and he knew little or nothing about sound theory or instrument design. Yet, with an enthusiastic if eclectic staff that included a totally blind man with 'absolute pitch', the elderly son of a celebrated historian, a famous violinist, a London theatre manager and two eccentric dogs.³² Nonetheless he had managed to get a variation of the Fessenden system to sea with trials in the submarine B3.³³ (Another product of Ryan's work was a "much more sophisticated arrangement of five powerful and sensitive hydrophones by which they could approach an enemy and obtain her position without using the periscope.")³⁴ These arrays went into the R Class anti-submarine submarines of which 10 were completed just before or just after the end of WW1 but only two survived beyond 1923. However, they were not used to develop tactics for their intended role and the potential of the array was not explored. Later, the Germans used hydrophone arrays extensively; the Royal Navy not until asdic Type 186 in the 1950s.³⁵

Ryan's work resulted in two new designs: an improved Fessenden which became Type 102; and a transmitting-only version that was designed to talk to submarines under tow. WW1 submarines, including the E Class and L Class, were fitted out with the Type 102 but research continued with upgrades until 1931 when the S Class were fitted with Type 106X³⁶ operating at 1080 Hz.³⁷

Early outfits had two 5 inch plate hydrophones of a new design (either a Mark II, IV or V) and tuned to 900 Hz that were fitted in the submarine's pressure hull, both forward with one on either side.³⁸ By 1926, a third plate had been added, facing aft, "immediately abaft, or inside the after superstructure of the conning tower; it should, when possible, be placed not less than five feet above the pressure hull."³⁹

There were three principles behind the installation of this apparatus: safety, attack and navigation or tactical. For safety, it was considered possible to detect another dived submarine and so avoid collision. The attack mode was severely limited, and the submarine had to be swung across the bearing of the target to find the null point between the two forward hydrophones. Unsurprisingly, this was not considered to be very successful⁴⁰ so the deficiency was rectified by the later installation of the Revolving Directional Hydrophones (RDH). The navigational use was for the detection of the submarine bells and the tactical was the start of sound telegraphy (S/T sometimes later called S.S/T or SST)⁴¹ whereby a submarine could both listen to the message and get a bearing on the transmitting submarine. The thought was that this would allow submarines to operate together in, for example, a patrol line.

Ranges out to 20 miles for SST were claimed but reception could be seriously affected by ambient or own ship's noise.⁴² The advice was for the operator to listen on all three hydrophones at the same time especially if SST was expected and some of the principles for a passive search housekeeping that would last well into the future were laid down. For example: slow speed to reduce flow noise; casing rattles had to be eliminated; machinery to be stopped (apparently the hydraulic system particularly interfered); and the operator was to be informed of course and speed changes and pump starts/stops etc.

In submarines, the Telegraphists were used to operate SST and the hydrophones and had the post-nominal HL, for Hydrophone Listener. There were two reasons to use the telegraphists: the transmissions used Morse code (the Morse for the letter 'F' was used for ranging) and the W/T amplifier was used to amplify the hydrophones signal. This meant that the hydrophone switchboard was co-located with the W/T amplifier although a pair of headphones was provided in the control room for the captain and later an extension listening station was in the fore ends to keep the operator away from the machinery noises⁴³ but it was a monotonous work resulting in operator fatigue and the necessity for frequent changes of operator.⁴⁴ Submarines, of course, did not have large complements — the H32 had 42 crew members — so telegraphists probably found themselves watch and watch about. In 1920, such was the enthusiasm for asdics, that the General Service SD (Submarine Detector) branch was established being formed by selected seamen ratings under the age of 25.⁴⁵ In submarines the job was still done by Telegraphists, called Telegraphist Detectors, and trained as asdic operators at HMS Osprey in Portland⁴⁶ which had been established as the antisubmarine school in 1924. But as late as 1937 sufficient numbers of suitable telegraphists could not be >found; although it was hoped to resolve the situation by 1939!⁴⁷ The branches stayed like this until 1947 when both surface ship and submarine asdic operators became members of the Underwater Control (UC) branch.⁴⁸

The Revolving Directional Hydrophone

Towards the end of the war submarines began to be fitted with a set of revolving hydrophones positioned outside the hull. Initially this was supposed to be in the stem of the boat as shown, see Figure 1,⁴⁹ but this was amended to be on top of the forward casing as appears in Figure 2.⁵⁰ The apparatus consisted of two plate receivers, back to back, and connected by a rod. When either of the plates was pointing directly at the sound source there would be maximum movement on the rod and therefore maximum reception. Conversely, when both hydrophones were receiving the same amount of noise they would cancel each other out resulting in no rod movement and no reception. This was known as the 'minimum property' and was estimated to provide a bearing with an accuracy of ± 10°⁵¹. The plate hydrophones were more sensitive and could detect sounds to three times the range of the RDH hydrophones. Even so, the RDH had detected surface ships up to nine miles.

Figure 1: THE REVOLVING DIRECTIONAL HYDROPHONE
On the left the RDH is shown mounted above the casing at the stem of the submarine. The diagrams on the right show how the hydrophones need to be turned to determinebearing.

Figure 2: THE REVOLVING DIRECTIONAL HYDROPHONE

The RDH hydrophone can be seen ringed in front of the fin. This was an alternative position to that advocated in ADM 186/450 Handbook of Hydrophones in Submarines 1926 rather than the ADM 186/440 1924 position. The transmitting and receiving hydrophones are forward between the torpedo tubes and hydroplanes

The birth of the towed array?

The principal problem with hull mounted hydrophones was that own ship's noise and flow noise masked any detections and mariners were not too keen to be stationary while hunting submarines. At the suggestion of the Board of Inventions and Research (BIR), Ryan began investigating towing a hydrophone in early 1916. Others were also working on the problem, on 31 July 1917, GH Nash of the Western Electric Company claimed to have solved the problems of moving a hydrophone through the sea at speed without water noise, and how to hear and identify the direction of another ship totally submerged "or otherwise".⁵² He had developed the 'Fish' for the Anti-Submarine Division (he was reluctant to give it to the BIR because he had fallen out with them over a previous project). The 'Fish' had one bi-directional and one uni-directional hydrophone which rotated. Bearing was determined by the bi-directional hydrophone's minimum position and ambiguity resolved by the uni-directional hydrophone. There were other versions such as Cranston-Vanesbroeck's idea in 1915/16 which proved no better than that the readily available, petrol-filled hydrophone, (with no named inventor), and the Dawson Pendulum hydrophone which depended on the pendulum for stability.⁵³ It seems that Nash's invention, which was first tested in the swimming pool at Portland,⁵⁴ won the day, for 136 of his 'Fish' were initially ordered with an anticipated order of around 360 sets and Nash was awarded £3000 for his work.⁵⁵

But it was Ryan's 'Rubber Eel' that went into submarines. The Eel was 18 inches long by 3 inches in diameter and was omni-directional, the sound waves compressing the rubber body and passing through the internal jelly to the diaphragm where a microphone detected the vibration. It had a reel with 150 feet of cable mounted on the bridge rail and could be towed astern or over the side while the submarine was stopped. There is an indication, although no absolute proof, that the eel was towed dived.⁵⁶

Figure 3: THE LANCASHIRE FISH and THE RUBBER EEL
The Lancashire Fish is clearly much larger than the 18 inch long Eel and was a more sophisticated towed hydrophone. But it was too late to become operational during the war.

Research continued throughout the war on towed hydrophones resulting in an improved Eel, called the 'Porpoise', and eventually a sophisticated device called the 'Lancashire fish'. But none went into production before the war ended and the technology was not pursued further as was much of the research on hydrophones in favour of the advent of asdic.⁶²

The Inter-War Years and The Birth of Asdic

The conception and gestation period

The conception of asdic is murky and its gestation muddied. They involve an eclectic mix of British, Canadian, French and Russian scientists and engineers working in a wide variety of research establishments and companies. The three names most quoted are: Constantin Chilowsky, the Russian émigré who proposed an echo-ranging system using high-frequency sound waves; Paul Langevin, a leading French scientist who identified and introduced the efficacies of the quartz crystal to the transducer; and Robert Boyle, a Canadian scientist and protégée of Ernest Rutherford who persuaded Boyle to work for the BIR where he was charged with developing the work of Chilowsky and Langevin. It was Boyle's recognition of the wartime urgency and focus on producing a practical device that could be used at sea as soon as possible, rather than seeking scientific perfection, that wins him the accolade of being the "Inventor of Sonar".⁶³ Boyle made the breakthrough of getting an asdic echo from a submarine at 500 yards in 1918, but this used a separate transmitter and receiver. Three months later he was achieving the same results with a single transducer transmitting through a dome similar to the submarine RDH canvas covered, metal-lattice-framed dome which, it was discovered, caused only a small signal loss. The first ship-fitted asdic, Type 111, was fitted in HMT Ebro II just five days before the end of the war.⁶⁴ Unlike the other principals, Boyle did not take out any patents and later disappeared back into relative obscurity as an academic at the University of Alberta.

Secrecy

Following Boyle's breakthrough and then quickly following the end of WW1, everything to do with asdic now became shrouded in the utmost secrecy even to the extent that quartz was referred to as 'asdevite'. This concealment continued until 1929 when the Naval Staff decided that the term 'asdics' could be openly used65 but that installations still remained a secret and any reference to them had to be concealed as a secret in double envelopes.⁶⁶ This led to some farcical implications of the policy as Mayers relates. On one occasion he was given a double envelope marked secret. Furtively reading its contents it told him that "Submarines L53 and L543 [both asdic fitted submarines] had left Gibraltar and would arrive at Devonport on March 10". He then read the very same words in the Times newspaper.⁶⁷

The name 'asdic' only first came to the public's attention in December 1939 when Winston Churchill used it in the House of Commons. Mr RW Chapman, of the Clarendon Press, wrote to the Secretary of the Admiralty asking for clarification on behalf of Oxford Dictionaries. The Director of the Signal Department replied saying that the word derived from "the first letters of the words Allied Submarine Detection Investigation Committee, a body which was formed during the war of 1914-1918, and which organised much research and experiment for the detection of submarines".⁶⁸ However, as Hackmann points out, there is nothing in the archive to suggest that this committee existed. Rather, Hackmann avers, it almost certainly was derived from the title Anti-Submarine Division-ics.⁶⁹

In 1920 the 'Bonar Law Committee'⁷⁰ proclaimed that asdics and hydrophones were considered both as anti- and pro-submarine devices⁷¹ and with a reorganised Department of Scientific Research and Experiment (SRE, Admiralty) development continued to produce, by 1922, the surface ship Types 111 then 112, 114 and 115 retractable asdic sets.

The Development of Submarine Asdics: Types 113, 116, 118 and 120

The Admiralty did not wait for the Ebro II trials to even start before ordering 20 Type 111 asdic sets in June 1918 rather, they had put their faith in outboard trials that had been conducted in two whalers, Icewhale and the Cachelot. The P59 had the distinction of being the first warship to be fitted with an inboard asdic in 1919 and about the same time as the whaler trials it was achieving detection ranges of 1100 yards. The set was standardised into the Type 112 with a retractable cylindrical canvas dome shrouding a single ply quartz transducer operating at 20-50 kHz. The transducer was hinged so it could act as an echo sounder and the set was fitted in the ships of the first A/S Flotilla in 1920-21 to give them a maximum asdic-operating speed of 12 knots.⁷²

As the first ships were being fitted with the next version, Type 112, work started, in 1921, on the first submarine asdic - the Type 113 which was to be a Type 112 turned upside down so that both the dome and the 15 inch, four-ply transducer with an extra quartz layer and mild steel inter-plate, operating at 23.7 kHz,⁷³ were above the casing of the submarine although it was all retractable into a watertight compartment. This position gave the transducer a 320° listening arc, with a blind 40° created by the fin, and it enabled the submarine to operate the asdic when dived and bottomed, but not, of course, when on the surface. In 1922 the first asdic was fitted in the submarine H32 (Lieutenant WAC Dickson) for a lengthy period of trials.⁷⁴ This was Type113A, and H32 was the only submarine of her class ever to be fitted with asdic.⁷⁵ One of the first things the trials found was that the canvas dome was totally unsatisfactory and it was replaced almost immediately by a thin copper dome and then, after 1928, by mild staybrite steel. The copper dome was unpopular with the submariners of the day because, true to the traditions of the service, it had to be polished!⁷⁶

Figure 4: TYPE 113 ASDIC: SIDE VIEW; AS FITTED IN H32: CROSS SECTION
The hatch that can be seen on the left-hand drawing is probably from a later version as it is not visible on the H32.

The trials were Lengthy and extended trials followed covering the many potential uses of this new technology: station-keeping with another submarine; active range on the target; avoiding anti-submarine attacks; SST with both ships and submarines; and firing on an asdic bearing.⁹² One particularly interesting, and pertinent, trial was conducted a few years later when the H32 was invited to see if she could penetrate the columns in a convoy and make attacks using hydrophone effect and asdic. The H32 would detect the convoy by periscope and then go deep to conduct an attack by hydrophone effect (passive sonar in today's parlance) confirming range of the target by an active transmission. It was concluded that she did this "without any great difficulty" although the detection ranges in comparison to the later asdic sets were very low, 1200-1400 yards and self-noise was a big problem. The H32 also transmitted fairly frequently and these transmissions were intercepted by the convoy escorts. But the conclusions also warned against getting too close to the target because of the difficulty in differentiating between contacts. It also emphasised the necessity to go at slow speed to avoid self-noise interference.⁹³

Figure 5: ASDIC TYPE 113
FITTED IN AN
L-CLASS SUBMARINE

The Type 113 was fitted aft in the L Class submarines. Shown is the first operational streamlined canvas dome. The narrower end is facing forward.

With the experience of the first destroyer asdic Type 114, modifications were incorporated, and the set became known as Type 113X to go into the submarine X1 (Commander Phillip Phillips) in 1923.⁹⁴ Further modifications to the Type 113X (which was now operating at 21-25 kHz and shared the Type 102 transformer)⁹⁵ created the Type 113C which was fitted in the 12

Group III L Class submarines in 1925. By 1926 seven submarines had been fitted. In the L Class submarines, however, the set was positioned aft of the fin and was intended to have an all-round reception but the development programme for a sound reflector arrangement to achieve that ambition was being developed for the destroyer Type 115. This programme, however, was abandoned and so Type 113 ended its long operational life with the 5th Training Flotilla in 1937 as obsolete with outdated electronics.⁹⁶

The set was initially designed to use in the active mode for determining the range of a target but it was found to act as an excellent hydrophone and so by the mid-1920s it was used more often in the passive mode taking over from the older hydrophones.⁹⁷

With the advent of the O Class submarines designed for long-range operations (the Far East was in mind) work started in 1923 on the replacement for Type 113A even while it was still undergoing sea trials in the submarine H32. The replacement, known as Type 116, could only be operated with the submarine dived but not bottomed with the exception that the Oberon's set was modified so that it could also be used on the surface.⁹⁸ This asdic was not a success and it is not too hard to realise why. It had a long vertical tube that extended through the pressure hull at both the top and bottom of the submarine; it leaked, and the asdic office, invariably had water splashing about. True to the eccentricities of many submariners, one First Lieutenant carried an umbrella!⁹⁹ The upper transducer was covered in a galvanised steel dome and although the set was in many ways similar to the Type 113 it had more advanced electronics and a heterodyne unit for earphone amplification. Transmission was still by a Morse key but a phonic chronoscope, which was stopped and started electromagnetically, was introduced for ranging.

While being built the first three O Class submarines Oberon, Oxley and Otway had an asdic office built into them and the dome seatings were machined ready, but the Type 116 was not fitted until the submarines had been handed over between 1926-27.¹⁰⁰ By that time 10 submarines were fitted with asdic.¹⁰¹ The inadequacy of this asdic was shown in the Oberon in September 1939 when it contributed to the submarine been declared unfit for operations.¹⁰²

The Type 116 had conical reflectors to provide all-round echo detection and listening, but these reduced its range dramatically and were scrapped along with the upper transducer and long rod leaving just a lower transducer projecting from the keel. Its operating frequency was modified to 10 kHz and the dome covering the keel transducer was changed to staybrite steel. The electronics were also cleaned up.¹⁰³ In 1929 this modified set, became the Type 118, and was fitted to the second batch of O Class, the Parthian Class, K26 and the Rainbow Class

(nominated Type 118A).¹⁰⁴ Asdic Type 118 then became the standard inter-war asdic set and unlike some of the Type 113 fitted submarines remained operational until 1937. Some concern was expressed that this set may become damaged in shallow water especially when the submarine was forced deep causing a recommendation that a mechanism to raise it within 30 seconds should be developed.¹⁰⁵ There is no indication this was done, but Type 118 was soon superseded by Type 120 and then Type 129 which were both keel-fitted.

February 1932 saw the introduction of the Type 120.¹⁰⁶ This was an improved Type 118 with almost identical directing gear and dome but placed more efficiently closer to the bow. By 1938 all submarine asdics were operating at 10 kHz,¹⁰⁷ which now became the standard frequency until the end of the 1950s as it was a better frequency for underwater signalling.¹⁰⁸ The Type 120 was further updated with a 4-ply quartz transducer and electronics from the small ships' Type 123.¹⁰⁹

Type 120 was fitted in the River Class submarines, where it was known as Type 120A, some of the earlier S Class submarines¹¹⁰ and the minelaying submarines of the Grampus-class.¹¹¹ McKenzie gives a good example of the versatility of this asdic set when, in the days before radars in 1936, the Hong Kong-based River-class submarine Rainbow led the old destroyer HMS Bruce " through a long, narrow, tortuous Channel, with no buoys or lights to assist navigation." She did this by using her Type 120A asdic in the 10 kHz active mode transmitting continuously to get ranges of the numerous rocks and hazards.¹¹²

Echo Sounders

In the beginning submarines had to rely on the leadline for taking soundings. The C27 (Lieutenant Sealy) had to use hers in the most stressing of situations as she fought to make her escape from the Gulf of Riga in October 1917 following the German invasion of the Gulf of Riga Islands under Operation Albion. Having been in action against the main German units, the battleships Kronzprinz and König, and having torpedoed the transport SMS Indianola, she was feeling her way across the 'four fathom bank' south of Osel Island when she wrapped her leadline around her propeller. In the best traditions of the Submarine Service her leadline was replaced by wheel spanner and a string.¹²⁰

FIGURE 6: THE KELVITE MK IV

This sounding machine would have been fitted in the submarine X1. It needed a

Clearly it was not a good situation when submarines could only find the depth by touching the bottom when dived or using a leadline on the surface. In 1920 the then Captain Martin Dunbar-Nasmith therefore invented a submarine sounding apparatus. No record of what this apparatus looked like or how it worked has survived but it must have been successful for it was fitted to 133 submarines and Dunbar-Nasmith was awarded £600 for his invention.¹²¹ Not all submarines however, were fitted with the Dunbar-Nasmith apparatus. For example, the submarine X1 was fitted with a Kelvite Mark IV sounding machine supplied by Kelvin Bottomley & Baird Ltd in 1922.¹²² This could only be used on the surface with the use of a boom to keep the sounding wire clear of the submarine. Operationally it was clearly inconvenient.

The first half of the 19th century saw some experiments with the use of explosives to determine the depth of the sea but they were inconclusive.¹²³ Thereafter development of the echo sounder paralleled asdics, starting with Fessenden. Although the German, Alexander Behm¹²⁴ took out the first patent on an echo sounder, it too relied on an explosion like the earlier efforts whereas the first commercial echo sounder using an oscillator was installed on the SS Berkshire in 1924 by Fessenden's company, the Submarine Signal Company.¹²⁵

Asdics needed to find a way of automatically determining the time between transmission of the signal and reception of the echo. The problem was the same for echo sounding, but more so because of the short duration between the transmission and reception and so, with the obvious commercial potential of an echo sounder, this development work took priority in the 1920s and the work moved from the Sheldon research site to the Admiralty Research Laboratory, Teddington, (ARL) in the austerity years following the war although its results were used in parallel with the development of asdic.

Out of various ideas, that of BS Smith whose echo sounder operated at ultrasonic frequencies prevailed, and in 1925 the licence to manufacture was given to Henry Hughes & Son (now Kelvin Hughes). The submarine Rover was the first naval vessel to be fitted with a production Type 752 in 1930 but it wasn't until six years later that a rotating stylus recorder was introduced.¹²⁶ This echo sounder was marketed he commercial version being identified for use in submarines.¹²⁷

It was this submarine echo sounder that created a milestone in asdic history when it was used to find the RMS Lusitania. In June 1935 the treasure-hunting company Tritonia Ltd. commissioned the SS Orphir, fitted with the British Admiralty M. S.II and a French Langevin-Chilowsky echo sounder to find the wreck.¹²⁸ The difference was that the British echo sounder could make a record of the search. The Admiralty echo sounder found the wreck most successfully which was then dived on later in the year although they were unable to recover anything of value.¹²⁹

Figure 7: BRITISH ADMIRALTY MS II ECHO-SOUNDER TRACE OF RMS LUSITANIA

The trace shows clearly the Lusitania standing above the seabed which has been scooped away on one side of the ship. The break in the trace is where the surveying ship, SS Orphir, went astern and the disturbance interrupted the sounding.

Type 752 was followed in 1937 by the Types 753 and 754, a deep, 130 fathoms, and shallow echo sounder respectively. By 1938 the Type 758N, with a quartz transducer was being supplied by Henry Hughes for all new construction submarines and in readiness for WW2 although it was used with caution operationally as it could be intercepted by hydrophones and asdics tuned to the same or near frequency. A 'snap-sounding' could counter this but the echo sounder was liable to give false readings from fish and water variations.¹³⁰ This echo sounder had a few modifications during the war the most notable being the development of long lasting impregnated paper.¹³¹ It was to be standard fit until it was replaced in mid 1960s by Type 773, a deep echo sounder, and Type 776 a shallow echo sounder which went into all classes of submarines. The Swiftsure Class, for example, had one Type 773 transducer and four Type 776 transducers, one in the keel, and three upward looking: one forward, one on the top of the fin and one on the rudder.¹³² In the early 1970s Types 778 10KHz, deep echo sounder and 780 were introduced all being produced by Kelvin Hughes.¹³³ The Type 780 was developed as a surveying echo sounder operating at 30 Khz and used for upward looking. Today's Astute Class have two Type 790 echo sounders which still record on paper rolls but there are seven transducers with an Intelligent Switch unit beneath the Recorder for transducer selection. Two 10kHz transducers in the keel are for deep soundings and they can operate in a continuous mode or 'single ping'. There are also two 33 kHz transducers also fitted in the keel for shallow water and a further three upward -looking transducers on the forward casing, top of the fin and top of the rudder. The Type 790 is to be replaced by the Type 800 made by SEA Ltd.¹³⁴ It's a long way from leadline to the Type 800's display screen.

Type 752 was followed in 1937 by the Types 753 and 754, a deep, 130 fathoms, and shallow echo sounder respectively. By 1938 the Type 758N, with a quartz transducer was being supplied by Henry Hughes for all new construction submarines and in readiness for WW2 although it was used with caution operationally as it could be intercepted by hydrophones and asdics tuned to the same or near frequency. A 'snap-sounding' could counter this but the echo sounder was liable to give false readings from fish and water variations.¹³⁵ This echo sounder had a few modifications during the war the most notable being the development of long lasting impregnated paper.¹³⁶ It was to be standard fit until it was replaced in mid 1960s by Type 773, a deep echo sounder, and Type 776 a shallow echo sounder which went into all classes of submarines. The Swiftsure Class, for example, had one Type 773 transducer and four Type 776 transducers, one in the keel, and three upward looking: one forward, one on the top of the fin and one on the rudder.¹³⁷ In the early 1970s Types 778 10KHz, deep echo sounder and 780 were introduced all being produced by Kelvin Hughes.¹³⁸ The Type 780 was developed as a surveying echo sounder operating at 30 Khz and used for upward looking. Today's Astute Class have two Type 790 echo sounders which still record on paper rolls but there are seven transducers with an Intelligent Switch unit beneath the Recorder for transducer selection. Two 10kHz transducers in the keel are for deep soundings and they can operate in a continuous mode or 'single ping'. There are also two 33 kHz transducers also fitted in the keel for shallow water and a further three upward -looking transducers on the forward casing, top of the fin and top of the rudder. The Type 790 is to be replaced by the Type 800 made by SEA Ltd.¹³⁹ It's a long way from leadline to the Type 800's display screen.

Figure 8: THE COMMERCIAL VARIANT OF TYPE752
The brochure cover. Inside it says that the MV Asturias was the first British	Type 752	Type 773 that replaced the Type	The latest echo sounder, Type 800

Asdics were a learning process

As asdic was developed, primarily for surface ships, during the interwar years the search for understanding as how to use the new technology and the natural insecurity in such a situation is all too evident in the documentation of the time. The influence of using asdic in an active mode, as in surface ships, and the propensity to manoeuvre numbers of ships in formations clearly permeate the thinking is how to best optimise the use of asdics in submarines.

The primary use of submarine asdic to benefit the attack as a complement to the periscope (not yet for a fully blind attack) prevails throughout much of the documented discussions. In second and third place are normally the avoidance of A/S vessels and then the use of SST for station keeping or communications in some form.¹⁴⁰

An exception to this order of priorities is in a December 1931 letter to the Admiralty from the Rear Admiral (S), Rear Admiral Charles Little¹⁴¹ just a couple months after taking up his appointment. He reveals the indecision as how best to use asdic despite asdic having been at sea in submarines for almost 10 years. He says: "the extent of the potential uses of the asdic are not sufficiently realised or appreciated". He then calls for a coordinated investigation of the potentialities of asdic. Little was a pre-WW1 submarine CO. During WW1 he had been either a Commander or Captain (S) and in that capacity he would have been aware of the introduction of the Fessenden hydrophones, their developments, and use in the SST role. But, between March 1919 and September 1931, when he became Rear Admiral (S), he had been mostly in Fleet, big-ship appointments rather than in a submarine appointment. This experience, or lack of interim submarine experience, may explain why the first priority for investigation was "To facilitate co-operation between Submarines whether on the surface or submerged." ¹⁴² This mindset of submarines cooperating is in the mode of Fleet manoeuvres rather than Doenitz's later Wolfpack operations and it is based upon active transmissions for SST. It is taken to the extreme a few years later, for, in 1936 instructions for a detailed choreography of a submarine flotilla formation of eight submarines is published.¹⁴³ This was despite divisional tactics having been discontinued many years earlier so clearly there was still some confusion.

Two reports following up on Little's letter remain to give us some idea of how COs are beginning to use the technology. A report from the CO of L27 in response to Little's letter indicates that he used his Type 113 mostly in a passive mode except for when he was forced deep and then used an active range to press home his attack. A common use was to try and jam the active asdic-fitted ships with the submarine's active transmission.¹⁴⁴ A later report recounts something of a more formal investigation or trial between the submarine L27 and the 6th Destroyer flotilla. Again, the CO had good results when using it as an active intercept set.¹⁴⁵

In 1935 the Rear Admiral (S), now Rear Admiral CP Talbot, again rewrote the priorities into an order that would prevail into WW 2: attack, anti A/S, SST, and navigation. Asdics had now adopted the 10 kHz as a standard frequency that would be used by the wartime Type 129.¹⁴⁶ By 1938, with the clear advent of war, and although there was a shortage of telegraphists to operate the asdic sets, asdic was being used confidently in a passive mode to help the attack solution. Propeller revolution counting was particularly commented upon as producing good results (75.6% within 1 knot). Similarly, submarines were getting up to 1 ½ minutes warning of an attack by an A/S vessel and although blind fire had not been particularly progressed, the use of SST was particularly accomplished: out of 520 exercises in SST communication 490 were successful.

Typical 10 kHz sonar performance at this time, (but not yet Type 129), is shown at Table 1. Submarines would be detecting surface ships passively at ranges often comparable to, or better than, visibility in the North Sea.

With this background the Submarine Service entered WW2.

The Wartime Asdics Type 129 and Type 138

The asdic that was to become familiar to all the WW2 submariners was the outstanding Type 129. First trialled behind a dome in the front end of the keel of HMS Seawolf in 1937, in 1938 it was decided that the set would be adopted as the standard submarine set.¹⁵⁶ This was, of course, just in time for it to be available for all the new construction submarines of the T Class, U Class, and V Class and their participation in WW2.

Operating at the now standard 10 kHz it was fitted in a cylindrical cage with a streamlined dome underneath the forward torpedo tubes at the forward end of the keel with an electric motor inside a watertight tank that was itself inside the pressure hull. This enabled the oscillator unit to be pulled inside the submarine for maintenance, repair or exchange. The Torbay (Lieutenant Commander Anthony Miers) achieved this at sea by isolating the fore ends, putting a pressure in the compartment to counteract sea pressure, opening the hatch over the tank withdrawing the oscillator and re-shutting the hatch. With the oscillator repaired, the process was repeated in reverse. All this happened in the Mediterranean, in April 1941, at night, on patrol in enemy waters. As Chapman points out, others would have waited until they were back in harbour but to fix it in this way was indicative of Miers' determined attitude.¹⁵⁷

Figure 9: ASDIC TYPE 129 FITTED IN HMS SENTINEL

Type 129 with Type 138 were the standard sonars in British submarines throughout WW2

FIGURE 10:
THE GILL PROPELLER

Invented by Major Gill in WW1 shrouded propellers were not used again until the

The Type 129 was gyro stabilised and intended as an attack set. Like its predecessors, it was often seen for its SST capabilities where, in the early versions, transmission was by Morse key and ranging was done by chronoscope but the sets were soon modified to have a range recorder, A/S3, with automatic transmission. There is little evidence to suggest that its use in this role was often, if at all, practised but it was certainly used on occasions, especially in the Mediterranean. However, from empirical, operational experience it was realised that the set acted as an excellent slow-rotating, all-round directional hydrophone and when it was coupled to the hydrophone arrays it was particularly good in the passive mode at 10 kHz. This capability introduced the art of determining a target speed by propeller revolution count¹⁵⁸ it also meant, however, that submarines needed to reduce their self-noise. The biggest culprit in this area were the submarine's own propellers and trials had been conducted shortly before the war to try and reduce this noise source. One trial in two S Class submarines involved using a Gill "hydraulic propulsion mechanism" ¹⁵⁹ which appears to be shrouded, helicoidal propellers, developed during WW1 by a Major Gill.¹⁶⁰ The shroud was effective at lower speeds but was abnormally noisy at higher speeds.¹⁶¹ Another was to change the asdic motor's alternator. It was found that the Germans could detect the set's alternator on their hydrophone arrays. When the alternator was changed the set became Type 129K and it was trialled in the captured German U-boat, U570, HMS Graph. The trial concluded that the set was comparable with the German hydrophone arrays. ¹⁶² Another solution, not to reduce self-noise but to avoid it in the U-class, was to put a second listening position in the fore ends as far away as possible from the diesel engines when the submarine was on the surface. But a much more comprehensive solution came with the T Class submarines which had their machinery resiliently mounted.¹⁶³

Extensive trials were conducted to determine the capability of the Type 129 in all its modes. It was found to be a very capable asdic intercept set achieving ranges out to 10 miles on a transmitting ship if the set was tuned to the frequency of the ship's transmitting asdic. SST, considered to be a very important aspect of asdic, was particularly successful with 490 out of 520 attempts being successful under 50,000 yards. The average range between two dived submarines over 137 exercises was 14,600 yards. Even with the submarine sitting on the bottom SST communications were maintained out to three miles.¹⁶⁴ With the submarine dived and at under 3 kts, in the asdic, transmitting mode, a merchant ship could be detected at 3400 yards and a submarine at 2900 yards if they were below 16 knots. Hydrophone effect ranges were out to between about 13,000-18,000 yards on an escorted target and 4000 yards on a submarine.¹⁶⁵

Because of its position the Type 129 had a blind stern arc so from 1943 a passive, manually-trained, listening-only, hydrophone called Type 138 was added to cover the blind arc and complement Type 129.¹⁶⁶ In the T Class the Type 138 was fitted on the after casing between 9 and 10 tubes. This position meant that the set had to be accommodated in the engine room where of course there was little spare room anyway and so its intrusion caused considerable problems.¹⁶⁷

The Type 129 went through many modifications one of which was to add a Mine Detection Unit (MDU). The MDU probably came about as a result of the mining of HMS Hunter off the coast of Spain during the Civil War which triggered research into mine detection.¹⁶⁸ It first went into the Triad in 1940¹⁶⁹ and then two further mine detection sets were developed during the war, the first, in 1943 the Type 148 operating at 40 kHz and the second, later towards the end of the war, the Type 152X, which was trialled in the Alcide. However, the first was not really used and the second did not get beyond its prototype stage.¹⁷⁰

The Type 129 was a most versatile asdic, its qualities ably exemplified by the experiences of wartime COs:

Lieutenant Hugh McKenzie¹⁷¹ relates, when as CO of the Thrasher in 1941, and off Benghazi in the Mediterranean, he also used the MDU to keep the boat away from minefields that lay either side of the Benghazi approach channel which he was trying to penetrate.¹⁷² McKenzie also used it successfully for SST communications with the Upholder at a range of eight miles in the Gulf of Taranto.¹⁷³ He also tried and make contact with the Upholder (Lieutenant Commander David Wanklyn VC) on 14 April 1942 after hearing her taking an intensive depth charging in the Gulf of Sirte. Alas, there was no response, Upholder had been sunk.¹⁷⁴

Commander Ben Bryant used the MDU this to effect in the Safari. As he was creeping up the coast of Yugoslavia in October 1943 he tracked the minefield which was to seaward of him.¹⁷⁵

Lieutenant Commander Mervyn Wingfield, CO of the Taurus, having sighted a Japanese U-boat while on the surface in November 1943, had to go deep because of the light and then used his Type 129 in the hydrophone effect or passive mode to complete the attack by firing a salvo of six torpedoes - one of which hit and sank the submarine I34.¹⁷⁶

Perspicaciously, Lieutenant James Launders, CO of Venturer used his Type 129 for an hour, again in the hydrophone effect mode, while he stalked the U-864 off Norway on 9 February 1945 before making history by being the first and only submarine so far to sink another submarine while both were dived.¹⁷⁷

The 129/138 combination continued at sea until the early 1950s being fitted in submarines of seven other different nations.¹⁷⁸ After the war the Type 138 passive set was given an active capability and renamed 138F. This set was now capable of transmitting at 14kHz for echo-ranging and SST and passive listening at between 500 Hz to 4.5 kHz. However, submarine operations were soon to change after WW2 and it was realised that something more sophisticated was needed¹⁷⁹ and that would need scientific and technical research.

Post WW2 and the start of the Cold War

The scientific community re-organise for the Cold War

The first thing to happen following the war was that the research organisations reorganised. The association between Portland and asdics/sonar had started as HMS Sarepta, the Experimental Hydrophone Establishment in 1917 which became the antisubmarine establishment under Captain S D Tillard, a survivor of the Hogue sinking in 1914 and Jutland. He was in command of HMS Osprey, an old whaler and leader of the 1st Anti-Submarine Flotilla in 1924.¹⁸⁰ By this time the antisubmarine school had 13 officers training officers and asdic operators at Portland and HMS Vernon¹⁸¹ but in 1927 the school became a permanent establishment ashore at Portland.¹⁸² Tillard argued for the co-location of the various research establishments and a closer relationship with his antisubmarine school. This proposal received a sympathetic hearing and in 1927 the first Chief Scientist, B S Smith, was appointed,¹⁸³ an appointment that heralded, with the exception of a short move to Scotland during WW2, an association between Portland and sonar research until the end of the century. On return to Portland in 1946 the establishment was named the Anti-Submarine Experimental Establishment and then from 1947 the Underwater Detection Establishment (UDE). In 1959 it was decided that Portland would also become the home of scientific research into weapons, detection and control systems and the Admiralty Underwater Weapons Establishment (AUWE) was formed embracing UDE and the Admiralty Gunnery Establishment. At its height it had 93 Naval staff and 1,741 civilians of which 462 were of professional grades and 346 craftsmen.

Figure 12: UNDERWATER SYSTEMS RESEARCH ORGANISATION AND HISTORICAL ROADMAP FROM GOVERNMENTAL LABORATORIES TO INDUSTRY

The Admiralty's research establishments went through a number of reorganisations with their growth following WW2 and the increased research requirement for the Cold War. Equally, the establishments then had to go through a further reorganisation with the end of the Cold War and the shrinking research budgets.

Over the following years the Ministry of Defence's research organisations up and down the land were to go through several organisational iterations and mergers. First the Admiralty's research establishments were merged to form the Admiralty Research Establishment (ARE) in 1984. In 1991 as the "Peace Dividend" began to gain ground in Whitehall, all the main MoD's establishments were merged and split, the major part forming the tri-services Defence Research Agency (DRA) which was created as a sepa

Comments

Commander David Parry

David Parry joined the Navy in 1966 from the pre-sea training school HMS Conway. After Midshipman's time, half of which was spent in the submarine HMS Amphion, he joined the Submarine Training Class in 1970. After Part 3 in HMS Narwhal he became the Navigator and then spent two years as Navigator of the Canadian boat HMCS Ojibwa. 'Third Hand' of HMS Andrew followed, then a sabbatical as navigator to Comstanavforchan before PWO (N) and HMS Conqueror as Navigator again.

After Perisher in 1978 he commanded HMS Opportune (1980-82) and then as XO of HMS Swiftsure until he damaged his back and left the Navy. On retirement David took an MA in Maritime History at Greenwich University. This led to the PhD for which these short histories provide background for a more extensive history of the Perisher.

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