This report is continuing the work presented in "A study of Electronic Warfare against cruise missiles - An overview", FOI-R-0320-SE, December 2002. The focus of this work is based on the question how to form a networkbased electronic warfare system (ECM) and especially with concern on how a ground-based system interact with terrain masking. The effect of the electronic warfare signal ought to be directed to minimize the side effects of non-purposed warfare against GPS-transcievers. This means that the ECM-equipment must be directed from a sensor that has accuracy for this purpose and it also means that this kind of ECM-system has the same disadvantages regarding targetdetection as a more traditional warfare system has. This study shows that even with 200 m masts on choosen points in terrain, you will get terrain masking, which will prevent the ECM-signal to get through. The speed of the cruise missile is important because the speed says how long the ECM can have effect. This means that the distances between nodes in the ECM-system must be short to prevent terrain masking and also that the equipment must be placed on high masts. Because of the long lapse of time the ECM must be effectful there is also a great need of depth in the network. A proper net could be the mobile telephone net because of the useful infrastructure if only higher masts could be used.