Describes two interacting two-sided expected-value computer simulation models for evaluating tactical airpower systems in air/ground combat. Ground-attack sorties from the air model TALLY are fed into the ground model TOTEM. TOTEM may feed back into TALLY if, for instance, ground forces overrun airbases. For each of two sides, TALLY considers in detail up to 100 airbases with 20 aircraft types, and plays out sorties the operator allocates to airbase attack, mobility interdiction, close air support, and battlefield or rear air defense. Weather conditions by zone affect both models. TOTEM uses five trafficability conditions, six defensive conditions, and six types of unit actions. Unlike other models, TOTEM computes actual damage (vehicles killed) by air attacks. As the war continues, conditions are adjusted accordingly. Specific examples are given including comparisons of measures of effectiveness, with 17 charts. Choosing measures of effectiveness still depends on judgment and taste. (Invited paper, Military Operations Research Society, June 1973.) 28 pp.