page_title: HMS Graph
section_title: Trials
hierarchical_section_title: HMS Graph / Royal Navy service / Trials
caption_attribution_description: The Navigation Officer in the Control Room of HMS GRAPH, formerly the German U-Boat U-570; she is in the Clyde undergoing trials.
context_page_description: HMS Graph was a German Type VIIC U-boat that the British Royal Navy captured during World War II. Commissioned as U-570 in Nazi Germany's Kriegsmarine in mid-1941, she was attacked and captured on her first patrol.
  She provided both the Royal Navy and United States Navy with significant information on German submarines, and carried out three combat patrols with a Royal Navy crew, becoming the only U-boat to see active service with both sides during the war. She was withdrawn from service in 1944 due to problems maintaining her. While being towed to the breakers for scrapping, she ran aground on the Isle of Islay, off the west coast of Scotland. Some of the wreck was removed as scrap but some wreckage remains there to the present day.
context_section_description: Once seaworthy, meticulous trials were conducted to measure every aspect of Graph's sailing and diving characteristics. Even the Zeiss binoculars found on board were carefully tested.
  Graph's safe diving depth was discovered to be 230 metres (750 ft)—much deeper than the British thought for this kind of boat. At the time, Royal Navy depth charges had a maximum depth setting of 170 metres (560 ft) so the Germans could dive out of their reach. Depth charges were soon modified to take account of this. The boat's acoustic and magnetic characteristics were examined by different Admiralty research establishments.
  The Allied technical experts found much to praise about her design and construction. Graph's auxiliary machinery was on rubber mountings, making her stealthier by reducing sound transmission into the hull. The British and the Americans who examined Graph singled out her Zeiss periscope for particular praise. The American officers who carried out her initial inspection in Iceland recommended it be copied as quickly as possible for possible US Navy use. Her underwater acoustic equipment was found to be a sophisticated array of hydrophones that was significantly better than the British equivalents. The main criticism of the boat was poor and cramped crew accommodation, which would degrade crew performance on long patrols.
  In mid-1942, Graph was carefully studied by the US Navy, which then had an interest in a new, smaller submarine that would be roughly her size – around two-thirds the length and half the displacement of the Gato-class boats that formed the bulk of the US submarine fleet. She was considered superior in many ways to the two experimental Mackerel-class, the existing class of small US submarine, but the project was dropped.
  Full-scale models of her pressure hull were constructed, and used during mid-1942 for underwater tests of experimental shaped charge anti-submarine bombs. In a highly secret British project, Graph was also used as a model for the construction of three, full-sized, mock-ups of the control compartment, wardroom and radio room of a Type VII U-boat. These were used to train specialist groups of sailors, who would form boarding parties whenever a damaged U-boat was blown to the surface. They were trained to operate a U-boat's ballast-tank valves, to reverse any scuttling attempts by the crew, and to search quickly for cryptographic equipment and documents.
caption: A Royal Navy Sub-Lieutenant works at the chart-table in the control room of Graph, February 1942
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