ARL 1945 - 1977

With the cessation of hostilities in Europe in 1945, a few of the GC&CS Bletchley Park mathematicians and statisticians spent periods of time at ARL, the most notable being Dr I.J. (Jack) Good (1959-62 at ARL) who together with Professor Donald Mitchie (the Artificial Intelligence pioneer) was responsible for the final form of the Colossus computer (Colossus II), when at Bletchley Park. A realisation was made, early on, that Numerical or Statistical Analysis had a part to play in furthering understanding of operational issues relating to sonar and the host platforms. Another mathematician, and acquaintance of Bletchley Park's most famous cryptanalyst Dr Alan M. Turing, Dr Alister G.D. Watson became head of the Submarine Sonar Research Group at ARL. In 1945 Alan Turing joined the National Physical Laboratory (NPL) ARL's next-door neighbours to design and develop the pioneer, programmable computer: Automatic Computing Engine (ACE).

In 1951, although submarine related work (principally their quietening, detectability & detection) was absorbing considerable resources, ARL was more than capable of responding to urgent needs. For instance, at the time of the tragic loss of HM Submarine AFFRAY, ARL scientist W. Rosse Stamp hastily designed and constructed a submersible enclosure for the camera of a Closed Circuit Television (CCTV) system. The equipment (the world’s first rapidly-deployable (portable) underwater viewing system) was embarked upon HMS RECLAIM and operated, by Rosse and Lionel ‘Buster' Crabb, without a single hitch, and ultimately made the initial identification of HMS/M AFFRAY at her final resting place. The system continued to provide great assistance to the diving operations during the lengthy investigation of the sunken submarine. More information of ARL's underwater CCTV.

Note Rosse Stamp was one of a number of staff from the Admiralty Photographic and Instrument Research Laboratories (known as April), Kensington, London that were accommodated at (newly acquired) Upper Lodge when it was absorbed into ARL in 1949. As a commercial diver for hire (at that point in time), Cdr Lionel Crabb assisted April with their work on underwater photography and cine-photography, and visited Upper Lodge when April became the Instrument (K) Group of ARL.

Such was the utility of the portable underwater viewing systems that it opened-up a whole new area of research at ARL. As a consequence, in January 1954, at the time of the de Havilland Comet G-ALYP (Yoke Peter) crash in the Tyrrhenian sea off the Island of Elba, ARL was once again called upon to provide underwater viewing equipment to aid the search; ARL's George Macneice was flown out and operated the system to great effect, embarked upon RFA SEA SALVOR.

Cold War

Undoubtedly the Cold War period was the busiest and most productive time for ARL. The nuclear age meant involvement in radiological defence. ARL staff developed a high level of expertise and were widely consulted following fruitful research and design of dockyard, ship and crew decontamination techniques that included spraying ships with seawater, and a bar of decontamination soap. The research also led to the development of portable radiation detectors and monitors for ships, and Film Badges and pocket dosimeters for sailors.

The work on ship, submarine and torpedo hydrodynamics undertaken by ARL’s Fluid Dynamics Group demanded better facilities, which were constructed on the Upper Lodge site following its acquisition by ARL in 1945. The successful use of a small-scale Rotating Beam Channel (RBC) and a 12” working section Water Tunnel for studying and developing the theory of the water flow around bodies and propulsors, led to larger versions of both (ten times larger RBC & 30” Water Tunnel) being constructed on the site and operational by the mid-1950s.

New hydrodynamic facilities at Upper Lodge, from left: RBC, office block & 30" tunnel

These facilities were instrumental in the design and development of the control and propulsion of ships, submarines and torpedoes. The main thrust of the work was to make them considerably quieter in operation by the reduction of cavitation and flow noise; a significant source of noise is the cavitation caused by propeller blades. The control and pump-jet propulsion for the lightweight torpedo STINGRAY was developed using the facilities at Upper Lodge. STINGRAY was the first UK torpedo to be equipped with such propulsion; subsequently the heavyweight torpedo SPEARFISH benefited from the work.

Post-WWII ARL research into machinery noise sources, propeller cavitation and long-range passive sonar came together in the design and construction of a new class of conventional (Diesel-Electric powered) submarine: the PORPOISE class of the late 1950s known as P-Boats. Their propellers were specifically designed for reduced noise by delaying the onset of cavitation. Propeller cavitation, arising from high rotational speeds, is a particularly loud source of noise that is easily detected. Both main and ancillary machinery noise reduction together with quiet propellers resulted in their radiated noise when snorting being a staggering 3% of what was previously the norm. Further, they were virtually undetectable when submerged and running on electric-drive. They and the similar, slightly later OBERON class (known as O-Boats) were the quietest of all NATO submarines and substantially quieter than Soviet submarines. Their quietness in operation made them ideal platforms for the ARL-designed long-range passive sonar, Sonar 2007 - prototype versions (codenamed SOAP Stage II) were extremely successfully trialled in HM Submarines SEALION (P-Boat) and OTUS (O-Boat) in 1965-6. The sonar, SOAP, was the culmination of ARL’s work started by the Acoustics Group (and continued by the Submarine Detection Group from 1959 to 1978) that dramatically expanded post-WWII as Passive sonar (long-range detection by listening for the noise radiated by other vessels) became a reality.

Royal Navy OBERON Class Diesel-Electric submarine

Production version of Sonar 2007 fitted in the Sound Room of HMS/M OTUS

SOAP was based on innovative digital processing of the underwater sound received by hydrophones (underwater microphones) fitted along the sides of the submarine. The digital processing concept was proven under an ARL investigation into long-range (>100 miles) submarine detection systems with large hydrophone arrays sited on the seabed connected to land-based processing and display in the Shetland Isles (codenamed CORSAIR), over the period 1952-7. Initial work on submarine-borne long-range passive sonar was commenced under the codename KNOUT, and involved multi-hydrophone arrays (topside arrays) experimentally fitted to the casing of T-class submarines HMS/Ms TIRELESS and THULE. The first service version of this system was engineered by HMUDE, Portland as Sonar Type 186. The signal processing of Type 186 produced a single fixed (unsteered) beam that meant the submarine had to be manoeuvred to search a wider area. This transpired to be a severe operational drawback. By 1957, ARL was considering ways of including (in a submarine) the multi-look signal processing technique used at AES Unst (produced under the codename DICE) for the Sonar 186 array. The cross-correlating equipment known as DICE 1 was used successfully at AES Unst in the key exercise NIGHTSHADE – the operational assessment of prosecuting land-based CORSAIR detections using aircraft.

From the late fifties, the evolving circumstances demanded that ARL's approach become considerably more practical. The strive for quieter operation of naval vessels created high demands on ARL’s radiated noise measurement and analysis section of the Acoustics Group, and the mid-1950s use of portable noise ranges gave way to further permanent ranges located in Loch Fyne, Argyll, Scotland and the Inner Sound (between the Scottish island of Raasay and the mainland and based on the isle of Rona.

Having played a major role in the reduction of machinery and propulsion noise radiated by conventional submarines, it was very much a case of back to the drawing board as nuclear-powered submarines, capable of much higher transit and sprint (underwater) speeds, came into service. The main machinery of the first few generations radiated high levels of self-noise that demanded some radical thinking and new technology to reduce power generation and propulsion noise, to evade long-range detection by passive means.

The high levels of self-noise besides making them easily detectable also had a detrimental effect on the performance of the sonars fitted to the submarines; passive sonar (186 & 2007) was adversely affected by the ever-present noise, and active sonar (2001) similarly suffered degradation by the flow-induced noise arising from the higher operating speeds. Following the demonstration of the intrinsic worth (in terms of operational advantage) of long-range passive sonar on quietened conventional submarines, ARL commenced development (in 1969) of passive sonar towed array technology to provide a comparable capability for UK nuclear-powered submarines. The research created the foundations for modern sonar employing digital processing techniques developed by ARL using specially-designed hybrid analogue and digital equipment, and general purpose computers. A by-product of this research was bespoke high-resolution (acoustic) analysis equipment (designed by ARL) used by ARL’s Acoustic Intelligence Group and the joint RN and RAF acoustic analysis centre, based at Upper Lodge, these together were key Naval Intelligence units during the Cold War.

The other significant break-through came as a result of ARL fore-fronting the incredibly successful (radiated) noise reduction of nuclear submarines and torpedoes with the use of pump-jet propulsion. Pump-jet propulsion had important operational advantages over conventional multi-bladed propellers: they generated a fraction of the noise for the same thrust and were considerably more powerful. This was an American concept that scientists at ARL, together with engineers at the Admiralty Experimental Works, Haslar, Hants, made work and was subsequently sold back! Pump-jet propulsion was a major output of the hydrodynamics work undertaken at Upper Lodge and was first evaluated on TON-Class Minesweeper HMS HIGHBURTON; HM Submarine CHURCHILL was the first nuclear submarine to be propelled by pump-jet propulsion, in 1970. The hunter-killer SWIFTSURE Class of submarine (in-service 1973) was the first to be designed with pump-jet propulsion and this drove the adoption of a less-tapered aft section (offering increased internal space), which is now a common feature of submarines; thus UK nuclear submarines were decades ahead of their contemporaries.

The process of the reduction of noise from the main and the myriad of auxiliary machinery of a nuclear submarine also bore fruit as the sources of noise were (painstakingly) identified and evaluated by ARL. These were suppressed by component redesign and with the use of rafts and flexible couplings; further reduction was achieved by sound absorbent and anechoic coverings, which ultimately led to their use on the outer hull of submarines.