 The GHG had 24 hydrophones, the "Balkongerät" had 48 hydrophones and improved electronics, which enabled more accurate readings to be taken.It was one of less than ten submarines that the Germans outfitted with experimental synthetic rubber skin of anechoic tiles designed to counter Allied sonar devices.Codenamed "Alberich," after a sorcerer from ancient Norse mythology, this top-secret rubber coating process ultimately contributed to the ship's survival under extreme combat conditions and earned it the name "Black Panther."