Maintaining good hospital records during military conflicts can provide medical personnel and researchers with feedback to rapidly adjust treatment strategies and improve outcomes. But to convert the resulting raw data into meaningful conclusions requires clear terminology and well thought out equations, utilizing consistent numerators and denominators. Our objective was to arrive at terminology and equations that would produce the best insight into the effectiveness of care at different stages of treatment, either pre or post medical treatment facility care. We first clarified three essential terms: 1) the case fatality rate (CFR) as percentage of fatalities among all wounded; 2) killed in action (KIA) as percentage of immediate deaths among all seriously injured (not returning to duty); and 3) died of wounds (DOW) as percentage of deaths following admission to a medical treatment facility among all seriously injured (not returning to duty). These equations were then applied consistently across data from the WWII, Vietnam and the current Global War on Terrorism. Using this clear set of definitions we used the equations to ask two basic questions: What is the overall lethality of the battlefield? How effective is combat casualty care? To answer these questions with current data, the three services have collaboratively created a joint theater trauma registry (JTTR), cataloging all the serious injuries, procedures, and outcomes for the current war. These definitions and equations, consistently applied to the JTTR, will allow meaningful comparisons and help direct future research and appropriate application of personnel.