This document provides an overview of discrete event simulation (DES) and its benefits for decision support in defense applications. It discusses how DES can be used across a defense asset's lifecycle for requirements specification, concept development, tender evaluation, maintenance planning, and future demand analysis. The modeling process involves defining objectives, collecting and analyzing data, developing and verifying the model, analyzing simulation results, and providing recommendations. Examples of potential DES applications for defense include modeling future build programs and class transitions for manpower balancing.