We have performed a field experiment in the northern part of Mysingen of the Baltic Sea in order to determine the audibility of a sound source by a Towed Array Sonar (TAS). The sonar data were recorded at different source levels and under influence of the noise from the towing ship. The purpose of the experiment was to compare different algorithms for bearing determination and targeting. Our aim is to improve the detection and localisation performance by using advanced signal processing. In that way future submarines might have sufficient capability by using flank mounted antennas only and be spared of towing an array sonar. Two algorithms are compared with regard to the ability of targeting and to the bearing accuracy. These are a Kalman filtered synthetic aperture algorithm and a conventional beam forming method. In summary, the Kalman filtered synthetic aperture algorithm has better performance than the conventional beam forming method with the same sonar configuration. We also suggest further work in order to improve suppression of own noise.