To provide information about the performance and characteristics of effective and ineffective marginal personnel in the Army, a study has been made of about 1,800 men with experience ranging up to 20 years in five military occupational specialities (MOSs): 11E, armor crewman; 63C, general vehicle repairman; 76Y, unit and organizational supply specialist; 94B, cook. The sample included a comparison group of men in the same jobs but coming from the upper (nonmarginal) part of the Armed Forces Qualifying Test distribution. Performance was measured by intensive job sample tests, job knowledge tests, and supervisor ratings. Information about background, personal characteristics, and military experiences was obtained through biographical questionnaires, a battery of published and experimental tests, and Army records. First in a series, this report describes the rationale, research design, and general chronology of research events in the study. Twenty-two tables are included. (Author/LY)