problems solved before they entered Australian hands. The RAN began to realise that as the parent navy for the class, they had a greater responsibility than normal in ensuring that the boats were at an operational standard. Welding of Collins During assembly of Collins bow and escape tower sections in Sweden, multiple defects in the hull welding were discovered. Different reasons were given by different parties for the problems: To speed production, Kockums employed welders who were not qualified to work on high strength steels; the Qualified Welding Procedures developed by Kockums for these steels were not followed in production; the steel alloy used for the hull required different welding techniques to those normally used by Kockums; the Swedish navy always requested partial penetration welds for their submarines, while the RAN wanted full penetration welding, but had not made this clear; delays in delivering the steel plates to Kockums resulted in rushed work and a resulting drop in quality. Kockums engineers proposed that the section be kept in Sweden for repairs, but to minimise delays it was accepted as-is, with repairs attempted at ASC during full assembly of the first boat. Kockums sent welders and inspection technicians to ASC in order to assist in undertaking these repairs. However, when Collins returned to the ASC facility in April 2001 for a year-long maintenance docking, multiple welding defects were found in the bow and escape tower sections of the submarine (the two sections constructed by Kockums), while almost no problems were found in the welding of the four Australian-built sections. Repairing these welds quadrupled the time Collins spent in dock. Noise signature The noise made by the submarines, which compromised their ability to stay hidden, was another major problem with the design. In the original requisition, the RAN guidelines for the noise signature of the new submarines were vague; for example, asking that they be "twice as quiet" as the Oberons. Expectations and operational requirements also changed between the 1987 contract signing and when the submarines began operating in the late 1990s. The major element of the noise signature for the Oberon class was machinery noise transmitted through the hull; this was successfully avoided during construction of the Collins class by mounting machinery on platforms isolated from the hull. Noise testing during 1996 and 1997 found that the hydrodynamic noise signature—the noise made by a submarine passing through the water—was excessive, particularly