In the current sensor suites on board submarines the Passive Ranging Sonar (PRS) is a separate sensor, usually with three or more hydrophone groups on either side of the submarine. The aperture of this sensor is limited by the length of the boat, which makes ranging up to moderate distances possible. The combination of the towed and flank array sonar can be used to create a passive ranging sonar with a much larger acoustic aperture, resulting in a very long ranging capacity. Based on simulated data a calculation method was developed that combines adaptive beamformers, fine bearing estimation and a target localisation technique originating from an acoustic artillery ranging system. The method was evaluated on operational recordings of a towed and flank array sensor. If the target is detectable on both sensors, ranging can be performed instantaneous. The method is robust and can provide an increased passive ranging performance.