Nuclear propulsion was ruled out at an early stage of the project, because supporting nuclear submarines without a nuclear power industry in Australia and public opposition to such infrastructure would be extremely difficult. Air-independent propulsion (AIP) was also considered for the class, and the submarines were designed to be retrofitted with an AIP system. The AIP plan was cancelled in July 1996, after it was demonstrated during sea trials that during constant operations, the boat's snorkel was exposed for only a few minutes in a 24-hour period; officials from ASC claimed that any "Collins"-class submarine spotted while snorting would be because the boat was "dead unlucky". Installation of AIP was not believed to provide enough of an improvement on this to justify the predicted A$100 million cost.