HMS Graph - Royal Navy Service - Trials

Trials

Once seaworthy, meticulous trials were conducted to measure every aspect of Graph's sailing and diving characteristics. Her 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 the boat more stealthy by reducing sound transmission into the hull. In particular, her periscope was singled out for praise by both the British and the Americans who examined the boat. 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 submarines, the existing class of small US Submarine, but the project was dropped.

Full scale models of her pressure hull were constructed, and used during the summer of 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 were taught where to quickly search for cryptographic equipment and documents.