(FORTUNE Magazine) – Arguably the most aggressive pursuer of human enhancement is DARPA, the Pentagon's advanced research agency. In 2002 and 2003 it granted the author unusual access to many of its program managers and scientists. On these pages is a sampling of human-enhancement programs DARPA is sponsoring in labs and collaborations around the U.S.; media access to much of the work is now curtailed.

An Energizer Bunny in fatigues

GOAL: Soldiers who perform at unprecedented levels of physical intensity and maintain that intensity for extended periods.

HOW IT IS MEANT TO WORK: One project seeks to boost the power and efficiency of muscle cells (for details, see main story). Alternative approaches include controlling body temperature and tapping the energy stored in fat. Like athletes, soldiers get tired and slow down when they overheat; DARPA is testing gloves and booties that wick off excess heat from exercise, thereby stabilizing soldiers' core temperatures. To tap the energy in fat, DARPA is funding research on how to trigger a fat-burning mode that the body usually enters only when deprived of carbohydrates during starvation.

The sleep-free soldier

GOAL: Troops who can function effectively without sleep for a week.

HOW IT IS MEANT TO WORK: Today's techniques for keeping people awake usually involve the loss of cognitive ability. A DARPA-backed project at Wake Forest University centers on a novel class of medicines known as ampakines, which are thought to reverse chemical imbalances in the sleep-deprived brain. At Salk Institute, a project seeks to harness a natural antioxidant found in cocoa (Mars, the candy company, is a collaborator on that one). Scientists at the University of Wisconsin and other research centers are studying birds that migrate for days without sleep. Other groups are studying dolphins and whales, air-breathing mammals that would drown if they slept as we do and have evolved an ability to let one portion of the brain sleep at a time; DARPA hopes to enable troops to do the same. A related project at Columbia University is studying why some pathways in the human brain are much less susceptible to sleep deprivation than others; troops might be trained to use the resilient pathways to stay alert.

Control bleeding

GOAL: Soldiers who are able to stop bleeding at will.

HOW IT IS MEANT TO WORK: Several DARPA projects aim at severe wounds whose bleeding can't be stopped by direct pressure. Normally, blood clots in response to natural chemical cascades initiated by the nervous system; one proposed approach is to condition soldiers to consciously release the triggering chemicals--a soldier would be able to stop bleeding by concentrating on his wound. Another approach involves injecting vast numbers of nanotech magnets that would circulate harmlessly in the blood. In the event of injury, a special magnetic field passed over the wound would cause the magnets to align, forming a dam around which clotting would occur.

Pain control

GOAL: Soldiers who can simply block ongoing pain from an injury.

HOW IT IS MEANT TO WORK: The body has more than one neurological pathway for pain. The pain that causes you to jerk away your hand when you touch a hot stove involves a different pathway than the pain you'll feel later from swelling and inflammation. A "pain vaccine" under development by Rinat Neuroscience, a Genentech spinoff for which DARPA provided early funding, is designed to soak up secretions of a molecule called nerve growth factor that's necessary for the transmission of the second kind of pain. The vaccine is intended to remain effective for at least 30 days.

Limb regeneration

GOAL: Troops who, if wounded, can tap an innate mechanism to accelerate healing without scars and regrow lost limbs.

HOW IT IS MEANT TO WORK: A blastema--also called a regeneration bud--is a mass of undifferentiated cells that can develop into an organ or appendage. In salamanders and other lower vertebrates, blastemas regenerate severed limbs; young children sometimes regrow severed fingertips. DARPA wants to harness the genetic mechanism at work in blastemas to help injured troops. The research, once viewed as extremely speculative even by DARPA standards, lately gained renewed attention.