Action of 9 February 1945
Part of TheBattle of the Atlantic during theSecond World War
HMS Venturer in August 1943
Date 9 February 1945 (1945-02-09) Location OffFedje Island,Norway 60°46′10″N4°37′15″E / 60.76944°N 4.62083°E /60.76944; 4.62083 Result British victory
Belligerents
United Kingdom	Germany
Commanders and leaders
LieutenantJimmy Launders	KorvettenkapitänRalf-Reimar Wolfram †
Units involved
HMSVenturer	U-864
Casualties and losses
None	U-864 with all 73 hands

The GermanU-boatU-864 was attacked and sunk on 9 February 1945 byHMS Venturer, aV-class submarine of theRoyal Navy.Venturer was patrolling the waters aroundFedje Island, off theNorwegian coast in theNorth Sea. The sinking remains the only incident in the history of naval warfare where one submarine sank another while both were submerged.

HMS Venturer was aV-class submarine, longer than the earlierU-class with more rake on the stem. The boat was laid down on 25 August 1942 by Vickers Armstrong atBarrow-in-Furness, launched on 4 May 1943 and commissioned on 19 August. The boat had a complement of 37 men, including the captain, LieutenantJimmy Launders and had a maximum speed of 13 kn (24 km/h; 15 mph) on the surface. The boat was armed with four21-inch torpedo tubes with four reloads, a3-inch gun and three machine-guns.^[1]

U-864 was aType IX U-boat (KorvettenkapitänRalf-Reimar Wolfram) on a clandestine mission,Operation Caesar, to theEmpire of Japan.^[2] On 6 February 1945,U-864 passed through theFedje area off theNorwegian coast without being detected but an engine kept misfiring.^[3][a] There were many Allied (primarily British) ships, submarines and aircraft in the area on anti-submarine patrols. Wolfram decided to return to thepens atBergen to repair the engine.

The British were reading the GermanEnigma cyphers and the Royal Navy was concerned the secret cargo might enable the Japanese to extend the duration of thePacific War. When the British got the Enigma decrypts,Venturer, which was in the area, was ordered to destroyU-864. The Admiralty signalled toVenturer,

Important Secret U-boats probably use following routes: from 60°40' North, 004°26' East, Course 110° r/v off Hellisoy 1. Probable that U-boats proceed to seaward off r/v^[5]

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AsVenturer continued her patrol of the waters around Fedje, at9:32 a.m. the ASDIC operator noticed a faint Hydrophone Effect (HE) which faded, then came back forty minutes later, somewhat louder. After searching for another forty minutes a thin mast was spotted; to avoid giving away its presence,Venturer continued to use HE, which meant that only the estimation of the range of the periscope by the captain and estimation by the ASDIC operator based on the loudness of the HE.^[6][b] He tracked the U-boat's course by hydrophone and as the hydrophone plot emerged, it was noted that the U-boat was zigzagging. This made the German submarine quite safe according to the assumptions of the time.

18km
11.2miles

   

Location of the sinking

Launders tracked the U-boat for about three hours but it did not surface; Launders had to decide whether to attack before his batteries lost their charge. It was theoretically possible to compute a firing solution for time, distance, bearing and target depth but this had never been tried because it was assumed that performing the complex calculations would be impossible, plus there were unknown factors that had to be approximated. In most torpedo attacks, the target could be seen; the target's angle relative to the attacker and its bearing would be observed, then arangefinder in the periscope was used to establish the distance to the target; from this speed could be derived and a basic mechanical computer would offset the aiming point for the torpedo, the depth of which had to be set based on target identification. Too deep and the torpedo would pass under the target, too shallow (in this instance) it would miss above. Launders could only estimate the depth of his target as they tried to manoeuvre into a firing position without giving their position away by creating excessive noise or exhausting their batteries.

Launders made the calculations and assumptions aboutU-864's defensive manoeuvres, then ordered the firing of all four of his bowtorpedo tubes, diving immediately to avoid retaliation byU-864. The torpedoes were fired with a 17.5 second delay between each pair and at different depths.U-864 attempted to evade once it heard the torpedoes coming but lacked manoeuvrability in dives and turns; it took time to retract the snorkel, disengage the diesel and start the electric motors. The first three torpedoes were avoided butU-864 unknowingly steered into the path of the fourth.U-864 exploded, split in two and sank with all hands, coming to rest on the sea floor at a depth of approximately 490 ft (150 m).

U-864 sank 31 nmi (36 mi; 57 km) from the U-boat pens in Bergen. Launders was awarded a bar to hisDistinguished Service Order (DSO) and several members of his crew received awards.^[7] The action was the only naval engagement ever to have been fought entirely underwater.^[8]

• Akermann, Paul (2002).Encyclopaedia of British Submarines 1901–1955. Penzance: Periscope Publishing.ISBN 978-1-904381-05-1.
• Rohwer, Jürgen; Hümmelchen, Gerhard (2005) [1972].Chronology of the War at Sea, 1939–1945: The Naval History of World War Two (3rd rev. ed.). London: Chatham.ISBN 1-86176-257-7.
• Roskill, S. W. (2004) [1961].Butler, J. (ed.).The War at Sea 1939–1945: The Offensive Part II 1st June 1944 – 14th August 1945. History of the Second World War Military Series (pbk. repr. Imperial War Museum Department of Printed Books and Naval & Military Press, Uckfield ed.). London: HMSO.ISBN 978-1-84342-806-0.
• Walters, Derek (2004).The History of the British 'U' Class Submarine. Barnsley: Pen & Sword.ISBN 978-1-84415-131-8.

• "U-864: Hitler's Deadly Last Secret". History Television. Archived fromthe original on 27 September 2007. Retrieved28 May 2007.
• Helgason, Guðmundur."HMSVenturer".German U-boats of WWII – uboat.net.
• Helgason, Guðmundur."U-864".German U-boats of WWII – uboat.net.

• Battle of the Atlantic
• Naval battles of World War II involving the United Kingdom
• Naval battles of World War II involving Germany
• Submarine warfare in World War II
• Conflicts in 1945
• 1945 in Norway
• February 1945

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