This report describes Dyna-METRIC Version 4, a computer model that relates logistics resources and policies to wartime readiness. Developed for the use of logisticians to improve wartime logistics support, Dyna-METRIC assesses the effects of wartime dynamics and repair constraints and provides operational performance measures, problem detection, and spares requirements. Version 4 consists of five programs that provide for three echelons of interaction (including the depot-to-theater link) and three levels of components (for which demand processes, repair processes, and spares levels may vary). Dyna-METRIC portrays component support processes as a network of pipelines through which aircraft components flow as they are repaired or replaced within a single theater. Using the sum of all the pipeline segments, Dyna-METRIC determines the complete probability distribution for the number of parts in repair and on order. Combining the distributions for all components provides the estimate of aircraft availability and sorties.