between VARTA of Germany and Pacific Dunlop of Australia. These supply a single Jeumont Schneider DC motor, which provides 7,200 shaft horsepower to a seven-bladed, diameter skewback propeller. The propeller design is classified Top Secret, and must be covered before a Collins-class submarine can be removed from the water for maintenance. Emergency propulsion is provided by a MacTaggart Scott DM 43006 retractable hydraulic motor. The aft control surfaces are mounted on an X-shaped structure, giving the boats the ability to outmanoeuvre most warship and submarine classes. The Collins class has a speed of when surfaced and at snorkel depth, and can reach underwater. When travelling at , the submarines have a range of along the surface, or at snorkel depth. When fully submerged, a Collins-class submarine can travel at . 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. Sensors and systems The main sonar array is a Thomson Sintra Scylla active/passive bow sonar, linked to a passive intercept and ranging array distributed along the flanks of the submarine; three panels on each side. Collins and Farncomb were originally fitted with Thales Karriwarra passive towed sonar arrays, while the other four boats could be fitted with the Karriwarra or Thales' Namara array. These were later replaced across the class with the Thales SHOR-TAS towed passive array, deployed through the horizontal 'pipe' at the stern. When surfaced or at periscope depth, the Collins-class boats can use a Kelvin Hughes Type 1007 surface search radar, which is situated in a retractable mast on the fin. Each submarine is fitted with a CK043 search periscope and CH093 attack periscope. The periscopes were manufactured by Pilkington Optronics (now Thales Optronics), and experienced several problems early in