The most important role for U.S. strategic nuclear forces is to deter Soviet nuclear attacks by the threat of retaliation. Because of increased vulnerability of U.S. land-based missiles and the improved Soviet civil defense program, questions have been raised concerning the ability of U.S. forces to retaliate effectively in the future against the Soviet Union. Proposals to develop several new weapon systems to respond to these threats have been presented to Congress. This background paper, prepared at the request of the Senate Budget Committee, discusses the capabilities of both current and possible future strategic nuclear forces to destroy industrial and military targets in the Soviet Union after absorbing a massive Soviet surprise attack. Together with a companion paper, "Counterforce Issues for the U.S. Strategic Nuclear Forces," this study supports a forthcoming budget issue paper on strategic nuclear forces for fiscal year 1979. In accordance with CBO's mandate to provide objective analysis, the paper offers no recommendations. The paper is organized as follows: Chapter I - Why Measure Retaliatory Effectiveness?; Chapter II - Retaliatory Capabilities: How Many U.S. Weapons Would Survive a Soviet Attack?, How Many U.S. Weapons Would Reach Soviet Targets?, and How Much Damage Would be Inflicted on the Soviet Union?; Chapter III - The Effect of Soviet Civil Defense Measures: The Soviet Civil Defense Program, Effects of Population Protection Measures, and Effects of Industrial Protection Measures; Chapter IV - Retaliatory Force Structure: U.S. Retaliatory Force Options. Tables provide the following information: Estimated Characteristics of Current U.S. Strategic Nuclear Forces; Estimated Characteristics of U.S. Strategic Nuclear Forces in the Mid-1980s; Estimated Characteristics of U.S. Strategic Nuclear Forces in the 1990s; Estimated U.S. Strategic Forces Surviving a Hypothetical Soviet First Strike; and Retaliatory Capabilities of the Finite Deterrence Force.