How to decide in advance who will pass advanced military training

IT GOES WITHOUT saying that to be a marine you have to be tough, both physically and mentally. But which is more important? And, more specifically, which is the bigger obstacle to successful training? Working on behalf of America’s marine corps, Leslie Saxon, of the Keck School of Medicine of the University of Southern California, has been trying to find out.The elite of the marine corps is a group called Force Reconnaissance. These troops are employed in special operations, both “green” (in which having had to engage the enemy is deemed a failure) and “black” (where such engagement is the whole point). Initial training to join the force, open only to those already marines or naval doctors, lasts 25 days. Among other things it requires volunteers to tread water for nearly an hour, to run eight miles (12km) while carrying more than 50lb (about 23kg) of equipment, and to swim 100 yards (90 metres) with their hands and feet bound. Only half of those who volunteer for this training complete it. Of those who do not, roughly half are failed by the judges for posing a safety risk or for having a medical problem that stops them completing the course. The other half, though, drop out of their own volition.