Results of this study show that lightweight radioisotope heat sources can be considered for use undersea with little shielding necessary for electronics packages in close proximity to the heat source. Acceptable integrated electronic dose levels of 10 million rads for gamma irradiation and 10,000 reps for neutron bombardment were obtained for extended mission times for the three isotopes considered. Although it is unnecessary to shield the isotope Polonium 210 for electronic protection, its short half-life leads to heat management problems not encountered with either Cobalt 60 or Curium 244. For these latter isotopes, a shield around the electronics package is important to counteract the strong back-scattering effect of neutrons and gammas from surrounding seawater. Because the Curium 244 heat source apparently requires less shielding to electronics level, it would be more compact than the Cobalt 60 source. Retrieval of an isotope-powered undersea electronics package must be done remotely, and shielding provided to protect personnel engaged in retrieval, as well as in initial launching. 32 pp. Ref.