Anechoic tile

Their function is twofold: The technology of anechoic tiles was developed by the Kriegsmarine during the Second World War, codenamed Alberich after the invisible guardian dwarf of the Rhinegold treasure from Richard Wagner's Der Ring des Nibelungen music dramas.

[13][14][15][16] Anechoic coating based on research & technology supplied by Germany was also used by the Japanese I-400-class submarines, though completely different in composition from German rubber-based tiles like Alberich or Tarnmatte.

After the war the technology was not used again until the late 1960s when the Soviet Union began coating its submarines, starting with the Victor class, in rubber tiles.

[17] 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 signatures.

Modern Russian tiles are about 100 mm thick, and apparently reduced the acoustic signature of Akula-class submarines by between 10 and 20 decibels, (i.e. 10% to 1% of its original strength).

may consist of several layers of material with voids of variable sizes, designed to mask and deflect specific sound frequency ranges at different depths.

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.