 is limited to employing some form of energy detector. A large part of this chapter shall be devoted to discussing and comparing the merits of several different interceptor detector topologies which are important either because of their simplicity of implementation or because of their theoretically optimum performance capability. Such ability to employ a reasonably sophisticated signal feature detector, as opposed to, say, a sim- ple wideband radiometer, is a technique the interceptor is assumed to have at his disposal for improving his detectability. This is not to say that the enemy will necessarily employ this option since, in many cases, little or noth- ing is gained both from a performance and cost standpoint by using other than the simplest energy detector. In fact, in those situations, it may be Low Probability of Intercept Communications sufficient for the interceptor to jam the link between communicator and receiver SO as to force the communicator to increase his transmitted power aboce the level normally required for reliable reception, thereby raising his chance of being detected. The subject of enemy jamming of a communica- tor's transmission, with emphasis on the various system design tradeoffs pos- sible between the two adversaries, has been adequately treated in many of the chapters in Parts 1 to 3. Thus, we shall not repeat such discussion here in this chapter except in summary form in the final section. As is true for any scenario posed for a communication system design, the extent to which the interceptor can employ any or all of the above methods for improving his detectability is determined by factors involving both cost and complexity. Some mention of these factors will be included in our dis- cussion later on. Having briefly mentioned the various options available to the inter- ceptor, we complete our introductory picture by discussing the conditions and associated technologies which, when utilized by the communicator, greatly enhance his LPI position. For convenience of discussion we shall 