Quantitative estimates are developed of performance levels of selected U.S. Army combat crewmembers exposed to prompt ionizing radiation from nuclear weapons. The performance levels, expressed as percentages of normal (baseline) task performance, provide information for military operational planning, combat training, and computer simulation modeling of combat crew and unit effectiveness. A methodology is described using data from two separate bodies of information; (1) acute radiation sickness symptomatology, and (2) judgement of typical task performance time as recorded on army combat crew questionnaires. Those bodies of information are integrated to compute performance level as a function of dose (free-in-air) and postexposure time. Using radiation effects and symptomatology descriptions for each of eight separate dose ranges covering exposures from 75 to 4500 rads (cGy), we form a structure of symptom complexes in the dose/time domain extending 6 weeks after exposure to prompt radiation. Descriptions of symptom complexes used in the army combat crew questionnaires form the link between dose/time and the task performance estimates provided by supervisors of combat crews. We focus on soldiers representing four different crews, from the artillery (both gun and fire direction center crews), armor, and antiarmor, because their operations include the prospect of decisive encounters where one of the combatant crews will probably be put out of action. Keywords: Performance (human); Signs and Symptoms; Tactical Warfare; Combat Effectiveness; Antitank Weapons; Time Studies; Statistical Analysis; Tanks (combat vehicles); Nuclear Radiation.