German tanker Altmark Altmark was a German oil tanker and supply vessel , one of five of a class built between 1937 and 1939 . She is best known for her support of the German commerce raider , the " pocket battleship " and her subsequent involvement in the " Altmark Incident " . The Altmark Incident . " Altmark " ( Captain Heinrich Dau ) was assigned to support " Admiral Graf Spee " during her raid in the South Atlantic between September and December 1939 . Seamen rescued from the ships sunk by " Admiral Graf Spee " were transferred to " Altmark " . After " Admiral Graf Spee " was scuttled by her crew in the Río de la Plata in December 1939 , " Altmark " attempted to return to Germany , steaming around the north of Great Britain and then within the Norwegian littoral . On 14 February 1940 " Altmark " , proceeding south within Norwegian territorial waters , was discovered by three British Lockheed Hudson Mk . II ' s , from RAF Thornaby and pursued by several British destroyers led by . Late on 16 February 1940 in Jøssingfjord she was fired upon while the Norwegian Navy stood by and took no action save for raising a protest flag . The German tanker then received a boarding party from HMS " Cossack " . During an attempted escape across the ice , seven of the " Altmark " crew were shot down . During the skirmish " Altmark " was run onto the rocks . It had been the British intention to tow the ship back to a Scottish port , but the damage to the tanker ' s stern frustrated this idea . An attack by one belligerent upon its enemy in neutral waters is a breach of neutrality , in this case a breach of Norwegian neutrality by Britain . Because Hitler feared Norway would be insufficiently resolute to protect the German iron - ore traffic that passed legitimately along the Norwegian littoral , at Raeder ' s urging he decided on the invasion of Norway and Denmark in March 1940 . The British justification for the attack on the " Altmark " was set out in a Note to the Norwegian Government from Foreign Secretary Lord Halifax dated 10 March 1940 . The problem the British Government faced was the wording of The Hague Convention XIII of 1907 to which it was a signatory . Article 10 provides that : " The neutrality of a Power is not affected by the mere passage through its territorial waters of warships or prizes belonging to belligerents . " This meant that the " Altmark " was within its rights to sail through Norwegian waters with prisoners aboard providing that it did not come to a protracted stop longer than 24 hours . In the diplomatic letter , the British Government confirmed that it was not contrary to the law of neutrality to sail a prison ship through neutral waters , and Britain often did this herself . In fact the British complaint had nothing to do with the prisoners . " Altmark " was a Fleet tanker assimilated to a warship and was proceeding to Germany from the Atlantic by the north - about route . Instead of sailing down the North Sea as he would do in peacetime , the master of the " Altmark " had elected to sail the entire leg of the voyage southwards within Norwegian territorial waters in order to attract immunity from attack there under international law . There was no other reason for him to want to voyage through waters so dangerous to navigation . This must be an abuse of international law , and since the Norwegians had declined to stop the voyage the Royal Navy had done so on orders from the British Admiralty . The question remains unresolved to this day as to whether , as the Hague Conventions stood in 1940 , a warship could legitimately seek immunity from attack in neutral waters by widely varying its course to reach them . Subsequent history . The ship , renamed Uckermark on 6 August 1940 , then resumed in the role for which she had been built . During Admiral Lütjens ' Atlantic adventure with the battleships and between January and March 1941 , " Uckermark " ( Captain Zatorski ) was a supply ship and scout attached to the squadron . As the result of her reports the battleships were directed to various merchant vessels , which were then sunk . On 9 September 1942 she left France for Japan with a cargo of vegetable oil and fuel , supplying the auxiliary cruiser on the way , arriving at Yokohama on 24 November 1942 . " Uckermark " was then intended as the replenishment ship for the German raider , which was raiding merchant shipping in the Indian Ocean and western Pacific Ocean areas . On 30 November 1942 , " Uckermark " was anchored in Yokohama , Japan , next to " Thor " and the Australian passenger liner " Nankin " , which " Thor " had captured in March five days out from Fremantle , Australia , en route to Colombo , Ceylon . While the crew was at lunch , " Uckermark " suffered a huge explosion that ripped the vessel apart . " Uckermark " , " Thor " , and " Nankin " were sunk by the explosion . The cause of the explosion was thought to be a spark from tools used by a repair gang working near the cargo tanks . The Uckermark had delivered 5000ts of gasoline to Yokohama . It seems to be logical that the residual fumes and gasoline did explode . Diesel fuel does not explode the way the ship went up . 53 crewmen from " Uckermark " died in the explosion . The severely damaged ship was beyond repair and was scrapped . A number of survivors of the ship were sent to France on the blockade runner " Doggerbank " and perished when the ship was mistakenly sunk by the German submarine U - 43 on 3 March 1943 with all but one of the 365 strong crew lost at sea .