at high speed. The shape of the hull was the main cause: although a scale model of the design had been tested during the funded study and was found to have a minimal signature, the hull shape was changed after the contract was signed, primarily by a lengthening of the submarine and a redesign of the bow dome to accommodate the larger-than-expected main sonar and reduce its blind spot (the baffles). The design had not been retested, as who would pay for this could not be agreed on. Propeller cavitation, caused by water flow over control surfaces onto the propeller at certain speeds, was the other main noisemaker. Cavitation had not been a problem with earlier Swedish submarine designs or during early testing of the Type 471 design, but the propeller had to be redesigned late in the process to provide more power, and like the redesigned hull, was not retested. During the year 2000, an unusual meeting took place with a next door neighbor (Francis 'Frank' Smith) of the then HMAS Stirling Naval Base commander. He was an Aircraft Maintenance Engineer (originally trained at Government Aircraft Factories Fisherman's bend) who had been aware of the fluid dynamics issues of the Collins class for some time, purely by interest and observation on television. After a lengthy discussion, he was invited to discuss and demonstrate where possible, his observations at the Stirling Naval Base with Navy and Defence Science and Technology Organisation (DSTO) staff who were there at that time as part of an investigative group. He showed on a white board, the aerofoil issue with the Dorsal – Sail conning tower structure showing that the aspect ratio (span (height) to chord (width)) was too short and that severe turbulence / cavitation would be generated by such a design. This was demonstrated again on the white board using aircraft aerofoil wing shapes as a basis for the discussion. That the turbulence / cavitation generated would, by natural rearward flow, move down the rear upper surface deck of the hull and be drawn into the propeller. He was also able to demonstrate that the design of the bow section would not pass a flow test for generated turbulence / cavitation, with the change in shape from circular bow section to long hull, being ill-conceived. He made several recommendations during the lecture that would be cost-effective and possible. 1) To lengthen and taper