There is often a fine line between providing appropriate personal protection and compromising capability. In some situations, protection must come first. In other circumstances, capability becomes paramount. In the military, mission-specific objectives can force personal protection to be less than ideal. Indeed, levels of protection appropriate within the civilian context could jeopardise health and operational success, and for operations conducted in the heat involving load carriage and armored protection with almost total-body clothing coverage, it is the likely thermal impediment to performance that perhaps first comes to mind. Although this consideration is appropriate, it may direct attention away from the actual cause of, and therefore preventative solutions to, physiological collapse. For instance, although classical heat illness absolutely occurs at the age extremes, and it may affect all people when air temperatures are exceptionally hot, frank hyperthermia is not generally the primary cause of exhaustion when healthy clothed individuals are working in the heat. Instead, another homoeostatic process is implicated; blood pressure regulation. In addition to participating in temperature regulation, the cardiovascular system supports oxygen delivery, blood pressure regulatory, and waste removal requirements. Therefore, the elevated cardiac output accompanying work must be shared. Accordingly, the case will be developed that thermoregulatory failure is often not the primary causal mechanism for soldier collapse, although such individuals may be hyperthermic. Alternatively, moderately, but not excessively, hyperthermic soldiers working under these conditions are perhaps more likely to collapse from cardiovascular insufficiency that precipitates uncompensable hypotension.