The Dolphin Trucks (unique to PRR tenders) were designed to handle the high-speed passenger engine tenders (E6’s and K4’s) and light fright operation on the Pennsylvania Railroad. In 1913, PRR, E6 1067 was equipped with Dolphin Trucks and was extensively testing using seismograph equipment. This new design made both the engine and tender easier reading. Additional information can be found in, Apex of The Atlantics. Today only one E6 tender exist located at the Pennsylvania State Railroad Museum. See illustration in the Dolphin_Truck directory.