Anechoic tiles are rubber or synthetic polymer tiles containing thousands of tiny voids, applied to the outer hulls of military ships and submarines, as well as anechoic chambers. 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.