In fielding new weapon systems, the Military Services have experienced both quality and quantity problems with the spare parts. Poor design quality and poor manufacturing quality have produced spares with unexpectedly low reliabilities and result in increased parts demands. This overdemand combined with underbuying of critical spares has led to some significant impacts on availability, mission success probability, and sustainability for new systems. Spare parts requirements, like support and test equipment, are dependent on deployment and operation scenarios, and the configuration of the design. Use rates also drive spare parts needs. Technical risk (volatility of design) is an important factor in the purchase of spares. Supply support planning is an integral part of the overall logistics planning, and provides the mechanism for organizing, directing, and controlling the spares effort.