Although military doctrine assumes that thorough mission preparation is a prerequisite for mission success, empirical data are lacking. The present study investigated the relationship between mission preparation and mission performance during combat mission training of 11 MC-130P (Combat Shadow) aircrews from USAF Special Operations Forces squadrons. Two observers independently rated crew processes and mission performance based on extensive observations taken (a) during a planning period and (b) while the crews executed a simulated mission. A statistically reliable, strong relationship was noted between preparation and performance on a number of indices, with correlations ranging from .60 to .78. Notable preparation behaviors include utilizing personnel effectively, establishing a firm timeline, aggressively questioning a plan's assumptions, and testing a plan's logic against possible contingencies. The paper concludes with a discussion of the characteristics of effective mission preparation and implications for combat mission training.