procedures are followed, and the degree of coupling between procedures? Although there is some discussion of unit-level behavior moderators in this chapter, the focus is primarily at the individual level.
Interest in incorporating moderator variables such as task stress into military engagement simulations emerged in the late 1960s (Kern, 1966; Siegel and Wolf, 1969). In retrospect, these efforts were probably ahead of their time. For example, Siegel and Wolf's single-operator model incorporated a complex amplifying interaction between the level of operator capability and performance degradation due to time stress. Likewise, their multiperson model included such features as the costs of coordination as a function of the relative appropriateness of task allocation to team members. One of the factors that probably inhibited rapid elaboration of their models was the limits of computer capacity at that time.
There was renewed interest in moderator variables in the late 1980s. All branches of the military services supported associated research and system development efforts (for Army-supported efforts, see Van Nostrand, 1986; for Air Force programs, see Davis, 1989). Van Nostrand in particular opened several useful lines of inquiry. For example, she undertook to assemble and interpret data from Army field exercises that characterized the decline in soldier performance as a consequence of continuous operations, fatigue, and fear. In this regard, she was among the first to see the potential contribution of empirical data on soldier behavior under stress conditions to the development of a computational model of human behavior under battlefield conditions.
Van Nostrand also gave some quantitative specificity to the idea that morale can influence performance. She noted from various sources of military data that specific conditions, such as extremes in temperature, noise, the rate of friendly casualties observable by individual soldiers, and the turnover rate among unit members, had specific adverse effects on both individual and unit performance. Her work represents an attempt to examine and assess the state of the data from military studies on the relationship between external stressors and human behavior on the battlefield.
Davis' work at the RAND Strategic Assessment Center (1989) had a broader scope—incorporating theater-wide, strategic operations. This work was conducted in response to the hypothesis of military historians (see, e.g., Woldron, 1997) and users of war games that observable variations in large-unit performance can be linked to the character of commanders or the philosophical directives of particular cultures (see, e.g., Bennett et al., 1994).1 Davis' work addressed three broad factors: (1) fighting quality (different forces with equivalent equipment), (2) the friction of actual combat, and (3) the processes of command decision making in a particular political climate.