The U-864 was a Type IX D boat commisioned on 9 December 1943 by AG Weser in Bremen. U-864 was commanded its whole career by Korvettenkapitan Ralf-Reimar Wolfram. Wolfram had previously commanded U-108 (15 Oct 42 to 16 Oct 43) in which he made three patrols sinking one ship on his third patrol, he sank the American freighter 'Robert Gray' 7176 tons from convoy HX234.

  On 5 December 1944 U-864 set out from Keil as part of Operation Caesar, an attempt to prop up Germany's flagging Japaneese Allies by providing them with advanced technology including 70 tons of mercury, and jet engine parts. The boat set out through the Keil canal but grounded on the seabed and had to make an unscheduled stop at the Bruno U-boat pens at Bergen in Norway. The layover lasted longer then expected due to a raid on the pens and harbour on 12 Jan 1945 by 32 Lancaster bombers of the RAF. And in the meantime cryptographers at Bletchly Park had learned of the plans of Operation Caesar and U-864.

  The British submarine HMS Venturer, (commanded by Lieutenant James "Jimmy" S. Launders) was sent on her 11th patrol from the British submarine base in the Shetlands Islands out to Fedje.  After U864 messages had been decrypted, she was re-routed to intercept the U-boat. Meanwhile U-864 had left Bergen and on Feb 6th passed the Fedje area without being detected, but despite the repairs at Bergen one of her engines began to misfire and she had to signal the need to return to Bergen. U-864 recieved a signal that she would be sent an escort and was to meet it on 10 Feb. at Hellisoy.

  On 9 Feb. Venturer heard U-864's engine noise and spotted the U-boats periscope. The Venturer did not use her asdic so as not to give herself away. Launders then waited 45 minutes after first contact before going to action stations, waiting in vain for U-864 to surface and thus present an easier target. Upon realizing they were being followed by a British submarine and that their escort had still not arrived, U-864 zig-zagged in an attempted evasive manoeuvres and each submarine risked raising their periscope. After three hours Launders decided to make a prediction of his opponents zig-zag and release a spread of torpedoes into it's predicted course. The first torpedo was launched at 12.12 and then at 17 second intervals after that, and Launders then dived to evade any retaliation from his opponent. Three torpedoes missed but the fourth hit the U-boat splitting her in two and sending it to the bottom, going down with all hands. This is the only known case in naval warfare where one submarine sank another while both were submerged.

  There it lay until the Royal Norwegian Navy, alerted by local fishermen, found the wreck in early 2003. The mercury contained in 1,857 rusting steel bottles located down in the vessels keel, has started to leak and currently poses a severe enviromental threat.

  So far only 4 Kilograms of mercury per year is leaking into the surrounding enviroment, resulting in high levels of contamination in cod, torsk and edible crabs around the wreck. Boating and fishing around the wreck has been prohibited. Attempts to dig into the keel by robotic vehicles had to be abandoned after the wreck shifted. The delicate condition of the wreck, bottles and live torpedoes  would make trying to raise the wreck extremely dangerous. A three year study by the Norwegian Coastal Administration has recommended encasing the wreck in a 12 meter thickness of sand, with a reinforcing layer of gravel or concrete to prevent further erosion.

   Sources include www.uboat.net www.ubootwaffe.net  Wikipedia and other on line news outlets.