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.