German submarine U-480

German submarine U-480 was an experimental Kriegsmarine Type VIIC U-boat of World War II.

Considered by many to be the first stealth submarine, it was equipped with a special rubber skin of anechoic tiles (codenamed Alberich, after the German mythological character who had the ability to become invisible), that made it difficult to detect with the Allies' ASDIC (sonar). She was one of about six Type VIIs so equipped.

The U-boat was laid down in the Deutsche Werke in Kiel as yard number 311 on 8 December 1942, launched on 14 August 1943 and commissioned on 6 October 1943 under Oberleutnant zur See 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.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-480 had a displacement of 769 t when at the surface and 871 t while submerged. She had a total length of 67.10 m, a pressure hull length of 50.50 m, a beam of 6.20 m, a height of 9.60 m, and a draught of 4.74 m. The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2800 to 3200 PS for use while surfaced, two Siemens-Schuckert GU 343/38–8 double-acting electric motors producing a total of 750 PS for use while submerged. She had two shafts and two 1.23 m propellers. The boat was capable of operating at depths of up to 230 m.

The submarine had a maximum surface speed of 17.7 kn and a maximum submerged speed of 7.6 kn. When submerged, the boat could operate for 80 nmi at 4 kn; when surfaced, she could travel 8500 nmi at 10 kn. U-480 was fitted with five 53.3 cm torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.8 cm SK C/35 naval gun, (220 rounds), one 3.7 cm Flak M42 and two twin 2 cm C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.

Anechoic coating
Rubber foil containing air holes can be used to reduce the sound waves reflected under water by structures when foil thickness is small by comparison with the sound wavelength in water, providing a low reflectivity over a narrow frequency range.

The leading German acoustician Erik Meyer and his team developed a 4-millimetre (0.16 in) thick tile consisting of two 2-millimetre thick foils of synthetic rubber. The anechoic tile reduced echoes by 15% in the 10 to 18 kHz range. 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 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.

Other U-boats with the anechoic tiles coating include: GS U-11 (1935), GS U-485, GS U-486, GS U-1105, GS U-1106, GS U-1107, GS U-1304, GS U-1306, GS U-1308, GS U-4704, GS U-4708 and GS U-4709.

With the exception of U-480 and U-486, none of the other German submarines of this type with this equipment was lost in combat.

Service history
On its first patrol, the boat was attacked by a Canadian PBY Catalina flying boat of 162 Squadron RCAF, piloted by Laurance Sherman. The aircraft was shot down.

On the second patrol, Förster departed from Brest in occupied France on 3 August 1944, and sank two warships and two merchantmen:

For his success, Förster was awarded the Knight's Cross on 18 October 1944.

Fate
U-480 left Trondheim, Norway, on 6 January 1945 for its third and last patrol. It did not return. In 1997, the wreck of a Type VIIC U-boat was 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 identified as 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' sometime between 29 January and 20 February. A mine had damaged the stern 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.