first two submarines in late 1996, before completely re-designed seals were fitted to the boats in late 1997, solving the problem. The propellers themselves were also found to be poorly manufactured, having been shaped by hand, with at least one cast at the wrong pitch. This was rectified by using a five-axis milling machine for future shaping work and replacing the miscast propeller. The material used for the propellers was also found to be weaker than expected, developing fatigue cracks after only a few years of use. Instead of going to Kockums, which had started to go into decline after the end of the Cold War, the submarine project office sent the propeller to the United States Navy for redesigning. Despite the Americans fixing the problems with the propeller design, resulting in significant performance improvements, the Swedish company was dissatisfied with the Australian actions; the dispatch of the propellers was one of the points of contention in the company's legal action in the mid-2000s against the Australian government over ownership of the intellectual property rights to the submarine's design. Other propulsion problems included excessive motor vibrations at certain speeds which damaged various components (which was attributed to the removal of a flywheel and to corrosion caused by the fuel problems), and excessive fuel consumption in Collins at high speed (found to be caused by manufacturing problems with the turbines and turbochargers). The propulsion system was also found to be a secondary source of noise: poor design of the exhaust mufflers, weight-saving measures in the generator mountings, and an incorrect voltage supply to the battery compartment exhaust fans were noise-creating factors found and eliminated during studies by the DSTO. In March 2010, the Department of Defence revealed that the generators in five of the submarines were flawed and had to be replaced. The three generators aboard each of the five submarines are to be replaced in the submarines as they come in for their next maintenance docking. Periscopes and masts The periscopes had two problems, the first of which was shared with the other masts. They were not streamlined; raising a periscope while moving would create enough drag and turbulence to shake the entire submarine. As with many elements of the submarine, there were disagreements as to who was responsible for the problem. It was solved by modifying the masts to redirect the water flow around them (for example, a spiral