use as our model scenario the underwater or surface vehicle to satellite communication link. However, much of what follows is directly applica- ble to other scenarios such as communication between an airborne com- mand post and a satellite or surface ships communicating to airborne relays. First and foremost, the communicator must maintain as low a visual pro- file as possible, even when not communicating, to the extreme of completely concealing his location. Second, when transmitting, the communicator should reduce his radio detectability by minimizing his radiated power. The tech- niques available for accomplishing such include (1) specially designed low sidelobe antennas, (2) maximum use of channel coding to minimize the trans- mitter power necessary for proper message detection, (3) an optimum per- formance receiving system and, (4) low message bit rates and the shortest possible message lengths. Each of these are attainable to various degrees and the extent to which any of them may be employed depends upon the avail- able implementation technologies and costs. Finally, the communicator should employ SS modulation techniques to provide anti-jam (AJ) protec- tion against the interceptor. At this juncture, it is also worth pointing out that the communication receiver may itself attempt to jam the interceptor's receivers or otherwise confuse the interceptor by various decoy methods. Thus, the interceptor must be aware of this possibility and, if possible, guard against its occurrence. While all of the above factors individually contribute to a maximum LPI state for the communicator, it is possible that all may not be realizable simul- taneously. The reason for this is that some factors are both time and spatial dependent and the communicator may have little control over these when it becomes necessary to transmit. Variables of this nature might include (1) the transmitting antenna elevation angle when pointed to the communica- tion receiver (which depends upon the relative transmitter and receiver posi- Signal M