German submarine U-480

U-480 was an experimental Kriegsmarine Type VIIC U-boat of World War II, considered by many to be the first stealth submarime,it was equipped with a special rubber coating (codenamed "Alberich", probably after the German mythological character who had the ability to become invisible), that made it difficult to detect with British ASDIC (sonar).

The U-boat was laid down in the Deutsche Werke in Kiel as 'werk' 311 on 8 August 1942, launched on 14 August 1943 and commissioned on 6 October 1943 under Oberleutnant Hans-Joachim Förster.

U-480 carried out three war patrols, all under Förster's command. Because of its coating, the boat was sent to the heavily-defended English Channel. The Alberich worked; U-480 was never detected by sonar.

World War II service
On its first patrol, the boat was attacked by a Canadian PBY Catalina flying boat of 162 Squadron RAF, piloted by Laurance Sherman. The aircraft was shot down.

On the second patrol, Förster departed from Brest in occupied France on August 3 1944, and sank two warships and two merchantmen: For his success, Förster was awarded the Knight's Cross on 18 October 1944.
 * the Canadian Flower class corvette HMCS Alberni (K103) (925 tons) on August 21
 * the British Algerine class minesweeper HMS Loyalty (J217) (850 tons) on August 22
 * the Fort Yale (7134 GRT), sailing in convoy ETC-72, on August 23
 * the Orminister (5712 GRT) on August 25

U-480 left Trondheim, Norway on January 6, 1945 for its third and last patrol. It did not return. In 1997, the wreck of a Type VIIC U-boat discovered by accident by divers at 50.36778°N, -1.73611°W, 20 km southwest of the Isle of Wight. The following year it was correctly identified as the Alberich coated U-480 by nautical archaeologist Innes McCartney. Subsequent research by the Naval Historical Branch established that it had fallen victim to the secret minefield 'Brazier D2' some time between January 29 and February 20. A mine had damaged the tail of U-480, sending it to the bottom 55 m down. The entire crew of 48 was lost. Helmsman Horst Rösner only survived because he had been left behind in Norway for training.

The coating
The Germans developed a 4-millimetre (0.16 in) thick sheet of synthetic rubber that attenuated sound in the 10 to 18 kHz range to 15% of its normal strength. This frequency range matched the operating range of the early ASDIC active sonar used by the Allies. ASDIC's operating range would have been correspondingly reduced from its optimal range of 2000 m to somewhere around 300 m. The rubber contained a series of holes, which helped break up sound waves. There were problems with this technology: the material performed differently at different depths, due to the holes being compressed by water pressure, and securing the tiles to the submarine's hull required a special adhesive and careful application. The first tests were conducted in 1940, but it was not used operationally until 1944, with U-480. According to the Naked Science television episode "Stealth Submarine", U-480 had a perforated inner rubber layer covered by a smooth outer one. This formed air pockets with the right separation and size to muffle sonar waves.