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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. Types of polyisoprene ...

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

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

s, as well as

anechoic chamber An anechoic chamber (''an-echoic'' meaning "non-reflective" or "without echoes") is a room designed to stop reflection (physics), reflections or Echo (phenomenon), echoes of either sound or electromagnetic waves. They are also often isolate ...

s. Their function is twofold: *To absorb the sound waves of active sonar, reducing and distorting the return signal, thereby reducing its effective range. *To

attenuate In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable at ...

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 navigate, measure distances (ranging), communicate with or detect objects on ...

Development in the Third Reich

The technology of anechoic tiles was developed by the ''

Kriegsmarine The (, ) was the navy of Nazi 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 It superseded the Imperial German Navy of the German Empire (1871–1918) and the inter-war (1919–1935) of the Weimar Republic.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 military branch, branche ...

'' during the

Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

, 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, essayist, and conductor who is chiefly known for his operas (or, as some of his mature works were later known, "music dramas"). Unlike most o ...

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 . The compo ...

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 I. G. Farbenindustrie AG, commonly known as IG Farben, was a German Chemical industry, chemical and Pharmaceutical industry, pharmaceutical conglomerate (company), conglomerate. It was formed on December 2, 1925 from a merger of six chemical co ...

as a specially formed

synthetic rubber A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About of rubber is produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubber, just like natural ru ...

tile and made using a stabilized, non-polar, high molecular weight polyisobutylene 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 relating to the uniformity of a substance, process or image. A homogeneous feature is uniform in composition or character (i.e., color, shape, size, weight, height, distribution, texture, language, i ...

, 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 o ...

.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. Tarnung_U-480

The coating had its first

sea trial A sea trial or trial trip 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 op ...

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 around 250,000, it is Germany's largest city on the Baltic Sea. It is located on the Kieler Förde inlet of the Ba ...

performing tests in the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

. 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, Danish Straits that drain and connect the Baltic Sea to the Kattegat strait, which drains west to the Nor ...

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 advantage ...

had insufficient strength to bond synthetic rubber with the

pressure hull A submarine hull has two major components, the ''superstructure'' and the ''pressure hull''. The external portion of a submarine’s hull—that part that does not resist sea pressure and is free-flooding—is known as the “superstructure” i ...

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'', a branch of the ''Wehrmacht''. It was officially formed from the ''Marineleitung'' ("Naval Command") of the ''Reichswe ...

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, , 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 Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

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 or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a ...

, (i.e. 10% to 1% of its original strength). Modern tiles may consist of several layers of material with voids of variable sizes, designed to mask and deflect specific sound frequency ranges at different depths. Different materials may be used by marine engineers to cover sections of the submarine where they are needed to 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 naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

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