The Navy's proposed extremely low frequency (ELF) communications system (Sanguine), which would use an earthreturn circuit to excite the earth-ionosphere cavity, represents a potential electrical interference problem. The electromagnetic fields produced by Sanguine could influence other systems such as power distribution lines and telephone circuits, and other very long electrical conductors. This interference potential and the techniques useful in mitigating it are described. Also, data on power and telephone systems are presented that were useful in communications systems design tradeoff studies.