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Anechoic tiles are

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, and ...

or synthetic polymer tiles containing thousands of tiny voids, applied to the outer hulls of military ships and

submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...

s, as well as

anechoic chamber An anechoic chamber (''an-echoic'' meaning "non-reflective") is a room designed to stop reflections of either sound or electromagnetic waves. They are also often isolated from energy entering from their surroundings. This combination means ...

s. Their function is twofold: *To absorb the sound waves of

active sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on or ...

, reducing and distorting the return signal, thereby reducing its effective range. *To attenuate the sounds emitted from the vessel, typically its engines, to reduce the range at which it can be detected by

passive sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigation, navigate, measure distances (ranging), communicate with or detect o ...

Development in the Third Reich

The technology of anechoic tiles was developed by the ''

Kriegsmarine The (, ) was the navy of Germany from 1935 to 1945. It superseded the Imperial German Navy of the German Empire (1871–1918) and the inter-war (1919–1935) of the Weimar Republic. The was one of three official branches, along with the a ...

'' during the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, codenamed ''Alberich'' after the invisible guardian dwarf of the Rhinegold treasure from

Richard Wagner Wilhelm Richard Wagner ( ; ; 22 May 181313 February 1883) was a German composer, theatre director, polemicist, and conductor who is chiefly known for his operas (or, as some of his mature works were later known, "music dramas"). Unlike most op ...

Der Ring des Nibelungen (''The Ring of the Nibelung''), WWV 86, is a cycle of four German-language epic music dramas composed by Richard Wagner. The works are based loosely on characters from Germanic heroic legend, namely Norse legendary sagas and the '' Nibe ...

music dramas. The coating consisted of sheets approximately square and thick, with rows of holes in two sizes, and in diameter. Manufactured by

IG Farben Interessengemeinschaft Farbenindustrie AG (), commonly known as IG Farben (German for 'IG Dyestuffs'), was a German chemical and pharmaceutical conglomerate (company), conglomerate. Formed in 1925 from a merger of six chemical companies—BASF, ...

as a specially formed

synthetic rubber A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About 32-million metric tons of rubbers are produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubbe ...

tile and made using a stabilized, non-polar, high molecular weight

polyisobutylene Polyisobutene (polyisobutylene) is a class of organic polymers prepared by polymerization of isobutene. The polymers often have the formula Me3C H2CMe2sub>nX (Me = CH3, X = H, F). They are typically colorless gummy solids. Polymerization is typ ...

homopolymer with low-temperature elasticity; the rubber material itself was known by its trademark ''Oppanol''. The material was not

homogeneous Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...

, but contained air cavities; these cavities resulted in a degraded reflection of

ASDIC Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on or ...

.Rösler, Eberhard. ''Geschichte des deutschen U-Bootbaus, Band 2''. Bernard & Graefe Verlag. . The coating reduced echoes by 15% in the 10 to 18 kHz range. This frequency range matched the operating range of the early ASDIC active sonar used by the Allies. The ASDIC types 123, 123A, 144 and 145 all operated in the 14 to 22 kHz range. However, this degradation in echo reflection was not uniform at all diving depths due to the voids being compressed by the water pressure.Eberhard Rossler. ''The U-Boat: The Evolution and Technical History of German Submarines''. Cassell. An additional benefit of the coating was it acted as a sound dampener, containing the U-boat's own engine noises. The coating had its first

sea trial A sea trial is the testing phase of a watercraft (including boats, ships, and submarines). It is also referred to as a " shakedown cruise" by many naval personnel. It is usually the last phase of construction and takes place on open water, and ...

s in 1940, on , a Type IIB. , a Type IX, was the first operational U-boat with this coating. After its first war patrol, it put in at

Wilhelmshaven Wilhelmshaven (, ''Wilhelm's Harbour''; Northern Low Saxon: ''Willemshaven'') is a coastal town in Lower Saxony, Germany. It is situated on the western side of the Jade Bight, a bay of the North Sea, and has a population of 76,089. Wilhelmsha ...

probably sometime in April 1941 where it was given the coating. The coating covered the conning tower and sides of the U-boat, but not to the deck. By 15 May 1941, ''U-67'' was in

Kiel Kiel () is the capital and most populous city in the northern Germany, German state of Schleswig-Holstein, with a population of 246,243 (2021). Kiel lies approximately north of Hamburg. Due to its geographic location in the southeast of the J ...

performing tests in the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...

. During July, the coating was removed from all parts of the boat except the conning tower and bow. Further experiments and sound trials were made in the

Little Belt The Little Belt (, ) is a strait between the island of Funen and the Jutland Peninsula in Denmark. It is one of the three Danish Straits that drain and connect the Baltic Sea to the Kattegat strait, which drains west to the North Sea and Atlant ...

but they presumably proved unsatisfactory, as all the coating was subsequently removed. Problems were encountered early-on, when it was found that the

adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...

had insufficient strength to bond synthetic rubber with the

pressure hull A submarine hull has two major components, the ''light hull'' and the ''pressure hull''. The light hull (''casing'' in British usage) of a submarine is the outer non-watertight hull which provides a hydrodynamically efficient shape. The pressure ...

and casing. This resulted in the sheets loosening and creating turbulence in the water, making it easier for the submarine to be detected.Williamson, Gordon. ''Wolf Pack: The Story of the U-Boat in World War II''. Osprey Publishing; First Edition (2005). . Furthermore, the coating was found to have considerably decreased the speed of the boat. It was not until late 1944 that the problems with the adhesive were mostly resolved. The coating required a special adhesive and careful application; it took several thousand hours of glueing and riveting on the U-boat.McCartney, Innes.''Lost Patrols: Submarine Wrecks of the English Channel''. Periscope Publishing Ltd (2002). . The first U-boat to test the new adhesive was a Type VIIC. With good results with the new adhesive, the

Oberkommando der Marine The (; abbreviated OKM) was the high command and the highest administrative and command authority of the ''Kriegsmarine''. It was officially formed from the ''Marineleitung'' ("Naval Command") of the ''Reichswehr'' on 11 January 1936. In 1937 ...

intended that it would be widely used on the new Type XXI and Type XXII U-boats. However, the war ended before it could be put into large scale use. Ultimately only one operational

Type XXIII German Type XXIII submarines were the first so-called elektroboote ("electric boats") to become operational. They were small coastal submarines designed to operate in the shallow waters of the North Sea, Black Sea and Mediterranean Sea, where la ...

, , was coated with the anechoic tiles. U-boats with the anechoic tiles coating include: , , , , , , , , , , and .Wynn, Kenneth G. ''U-Boat Operations of the Second World War: Career Histories, U1-U510''. Naval Institute Press (1998). .Rössler, Eberhard. ''Die Sonaranlagen der deutschen Unterseeboote: Entwicklung, Erprobung, Einsatz und Wirkung akustischer Ortungs- und Täuschungseinrichtungen der deutschen Unterseeboote''. Bernard & Graefe. Anechoic coating based on research & technology supplied by Germany was also used by the Japanese submarines, though completely different in composition from German rubber-based tiles like ''Alberich'' or ''Tarnmatte''.

Modern day usage

After the war the technology was not used again until the late 1960s when the

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...

began coating its submarines, starting with the , in

tiles. These were initially prone to falling off, but as the technology matured it was apparent that the tiles were having a dramatic effect in reducing the submarines'

acoustic signature The term acoustic signature is used to describe a combination of acoustic emissions of sound emitters, such as those of ships and submarines. In addition, aircraft, machinery, and living animals can be described as having their own characteristic ...

s. Modern Russian tiles are about 100 mm thick, and apparently reduced the acoustic signature of s by between 10 and 20

decibels The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a Power, root-power, and field quantities, power or root-power quantity on a logarithmic scale. Two signals whose ...

, (i.e. 10% to 1% of its original strength). Modern materials consist of a number of layers and many different sized voids, each targeted at a specific sound frequency range at different depths. Different materials are sometimes used in different areas of the submarine to better absorb specific frequencies associated with machinery at that location inside the hull. The Royal Navy started using anechoic tiles in 1980, when was fitted with them during its second refit. The

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

also started using anechoic tiles in 1980, with . In recent years, nearly all modern military submarines are designed to use anechoic tiles.

References

Notes

{{reflist Stealth technology Submarine components German inventions of the Nazi period

Development in the Third Reich

Modern day usage

See also

References

Notes