During the past two decades the global security situation has seen some drastic changes. The operational scope of the Royal Netherlands Navy (RNLN) has expanded from operations on the open seas to operations both on the open seas and in littoral waters. A considerable part of the relevant operations now take place outside NATO territory. This shift in focus will result in an increasing number of expeditionary operations. Expeditionary operations consist of the following phases: departure – transit – arrival in the littoral – military operations in the littoral. Traditional anti-submarine warfare on the open seas is based on a mobile task group in transit in which the opponent’s operations are restricted by the speed of advance of the task group. After arrival in the littoral, however, the task group operates stationary, e.g. as part of a sea base. Such stationary operations are relatively new and new types of problems emerge: different types of threat may come from various directions, the possibility of blue-on-blue engagements increases, current sensor and weapon systems have not been optimised for stationary operations, etc.