A discussion of some of the basic concepts, measurement techniques, uses of data, and data-system implications involved in measuring missile reliability during the pre-launch phase of operations. A feasible reliability-measurement policy is outlined, and the ues of a weapon-centered missile status log to obtain reliability data is explained. The study provides a basis for critical reliability planning information required in both force-employment analysis and support-requirement calculations. It is a product of continuing work designed to improve the maintenance and operations of both manned aircraft and missile systems at the base level. Tables.