Anechoic tile
Encyclopedia
Anechoic tiles are rubber
or synthetic polymer tiles containing thousands of tiny voids, applied to the outer hulls of military ships and submarine
s, as well as anechoic chamber
s. Their function is twofold:
in the Second World War. Codenamed
Alberich after the invisible sorcerer from Germanic Mythology
. The coating was made up of sheets approximately 1 metre square and 4 mm (0.15748031496063 in) thick, with rows of holes in two sizes, 4 mm (0.15748031496063 in) and 2 mm (0.078740157480315 in) in diameter. It was manufactured by IG Farben
from a material known as Oppanol. The material was not homogeneous
but contained air cavities; it was these cavities that degraded the reflection of ASDIC. The coating worked in the 10 to 18 kHz range, reducing ASDIC to 15% of its normal strength. 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. An additional benefit of the coating was it acted as a sound dampener, containing the U-boat’s own engine noises.
The coating had it first sea trials in 1940, on , a Type IIB. U-67, a Type IX, was the first operational U-boat with this coating. After her first war patrol, she put in at Wilhelmshaven
probably sometime in April 1941 where she was given the coating, it covered the conning tower and sides of the U-boat, but not to the deck. By 15 May 1941, U-67 was in Kiel
performing tests in the Baltic Sea
. 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
but they presumably proved unsatisfactory, as all the coating was subsequently removed. Problems were encountered early-on, when the adhesive
was found to be not strong enough to stick the synthetic rubber sheets to the pressure hull
and casing of the U-boat. This resulted in the sheets loosening and creating turbulence in the water, making it easier for the submarine to be detected. 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. The first U-boat to test the new adhesive was U-480 a Type VIIC. With good results with the new adhesive, the Oberkommando der Marine
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, U-4709, was coated with the anechoic tiles. U-boats with the anechoic tiles coating include: , U-480, U-485 U-486, U-1105, U-1106, U-1107, U-1304, U-1306, U-1308
, U-4704, U-4708 and U-4709.
began coating its submarines in rubber
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
s. Modern Russian tiles are about 100 mm thick, and apparently reduced the acoustic signature of s by between 10 and 20 decibels, (ie 10% to 1% of its original strength).
The Royal Navy started using anechoic tiles in 1980, when was fitted with them during her second refit.
The US Navy started using anechoic tiles in the mid 1980s, with the improved 688-class submarine
USS San Juan
being the first boat to receive them. Nearly all modern submarines are now designed with them.
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
or synthetic polymer tiles containing thousands of tiny voids, applied to the outer hulls of military ships and submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s, as well as anechoic chamber
Anechoic chamber
An anechoic chamber is a room designed to stop reflections of either sound or electromagnetic waves.They are also insulated from exterior sources of noise...
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 the sounds emitted from the vessel, typically its engines, to reduce the range at which it can be detected by passive sonar.
Development by Nazi Germany
The technology of anechoic tiles was developed by the KriegsmarineKriegsmarine
The Kriegsmarine was the name of the German Navy during the Nazi regime . It superseded the Kaiserliche Marine of World War I and the post-war Reichsmarine. The Kriegsmarine was one of three official branches of the Wehrmacht, the unified armed forces of Nazi Germany.The Kriegsmarine grew rapidly...
in the Second World War. Codenamed
Code name
A code name or cryptonym is a word or name used clandestinely to refer to another name or word. Code names are often used for military purposes, or in espionage...
Alberich after the invisible sorcerer from Germanic Mythology
Alberich
Alberich was a legendary sorcerer who originated in the mythology or epic sagas of the Frankish Merovingian Dynasty of the 5th to 8th century AD, and whose name means king of the elves , who possessed the ability to become invisible...
. The coating was made up of sheets approximately 1 metre square and 4 mm (0.15748031496063 in) thick, with rows of holes in two sizes, 4 mm (0.15748031496063 in) and 2 mm (0.078740157480315 in) in diameter. It was manufactured by IG Farben
IG Farben
I.G. Farbenindustrie AG was a German chemical industry conglomerate. Its name is taken from Interessen-Gemeinschaft Farbenindustrie AG . The company was formed in 1925 from a number of major companies that had been working together closely since World War I...
from a material known as Oppanol. The material was not homogeneous
Homogeneity and heterogeneity
Homogeneity and heterogeneity are concepts relating to the uniformity or lack thereof in a substance. A material that is homogeneous is uniform in composition or character; one that is heterogeneous lacks uniformity in one of these qualities....
but contained air cavities; it was these cavities that degraded the reflection of ASDIC. The coating worked in the 10 to 18 kHz range, reducing ASDIC to 15% of its normal strength. 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. An additional benefit of the coating was it acted as a sound dampener, containing the U-boat’s own engine noises.
The coating had it first sea trials in 1940, on , a Type IIB. U-67, a Type IX, was the first operational U-boat with this coating. After her first war patrol, she put in at Wilhelmshaven
Wilhelmshaven
Wilhelmshaven 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.-History:...
probably sometime in April 1941 where she was given the coating, it 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
Kiel is the capital and most populous city in the northern German state of Schleswig-Holstein, with a population of 238,049 .Kiel is approximately north of Hamburg. Due to its geographic location in the north of Germany, the southeast of the Jutland peninsula, and the southwestern shore of the...
performing tests in the Baltic Sea
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
. 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
Little Belt
The Little Belt is a strait between the Danish island of Funen and the Jutland Peninsula.The belt is about 50 km long and 800m to 28 km wide, the maximum depth is approximately 75 m, and contains numerous small Danish islands....
but they presumably proved unsatisfactory, as all the coating was subsequently removed. Problems were encountered early-on, when the adhesive
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...
was found to be not strong enough to stick the synthetic rubber sheets to the pressure hull
Submarine hull
The term light hull is used to describe the outer hull of a submarine, which houses the pressure hull, providing hydrodynamically efficient shape, but not holding pressure difference...
and casing of the U-boat. This resulted in the sheets loosening and creating turbulence in the water, making it easier for the submarine to be detected. 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. The first U-boat to test the new adhesive was U-480 a Type VIIC. With good results with the new adhesive, the Oberkommando der Marine
Oberkommando der Marine
The Oberkommando der Marine was Nazi Germany's Naval High Command and the highest administrative and command authority of the Kriegsmarine. It was officially formed from the Marineleitung of the Reichswehr on 11 January 1936. In 1937 it was combined with the newly formed Seekriegsleitung...
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, U-4709, was coated with the anechoic tiles. U-boats with the anechoic tiles coating include: , U-480, U-485 U-486, U-1105, U-1106, U-1107, U-1304, U-1306, U-1308
German submarine U-1308
U-1308 was the last Type VII/41 submarine to be laid down, launched and commissioned by the German Kriegsmarine during World War II. The Oberkommando der Marine or OKM, , had decided near the end of World War II to put all of its resources into building newer types of Unterseeboot, such as the...
, U-4704, U-4708 and U-4709.
Use by the Soviet Union
After the war the technology was not utilized again until the 1970s when the Soviet UnionSoviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
began coating its submarines in rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
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
Acoustic signature
Acoustic signature is used to describe a combination of acoustic emissions of ships and submarines.-Contributing factors:The acoustic signature is made up of a number of individual elements...
s. Modern Russian tiles are about 100 mm thick, and apparently reduced the acoustic signature of s by between 10 and 20 decibels, (ie 10% to 1% of its original strength).
Modern usage
The 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 her second refit.
The US Navy started using anechoic tiles in the mid 1980s, with the improved 688-class submarine
Los Angeles class submarine
The Los Angeles class, sometimes called the LA class or the 688 class, is a class of nuclear-powered fast attack submarines that forms the backbone of the United States submarine fleet. With 43 submarines on active duty and 19 retired, the Los Angeles class is the most numerous nuclear powered...
USS San Juan
USS San Juan (SSN-751)
USS San Juan , a , was the third ship of the United States Navy to be named for San Juan, Puerto Rico. The contract to build her was awarded to the Electric Boat Division of General Dynamics Corporation in Groton, Connecticut on 30 November 1982 and her keel was laid down on 9 August 1985. She was...
being the first boat to receive them. Nearly all modern submarines are now designed with them.