In this paper the roles and functions of man in the evolution and development of two complex specific systems within the Army operational environment are discussed. It is pointed out that throughout the course of historical development, the basic system functions and objectives have remained unchanged even though the system equipments have varied. With equipment changes, man's physical functions in system operation have also changed. In predicting the effectiveness of man in a future system operational environment, an approach independent of equipment differences is required. Such an approach in which man is conceived as an information processor is described. The approach is applied to the human operator roles in manned aerial reconnaissance and surveillance and in targer acquisition. (Author)