(CNN) -- Forty-three soldiers suffered heat-related illnesses Friday during a 12-mile road march at Fort Bragg, North Carolina, an Army spokesman said.
The march was the culmination of a week of "expert field medical badge training," during which soldiers are tested on their medic and general soldier skills in order to receive an "expert" badge, Fort Bragg spokesman Benjamin Abel said.
Sixty soldiers were on the march, which started at 6 a.m., and they were carrying backpacks, helmets, weapons and other combat gear, Abel said.
About an hour and a half into the march, the people running the event noticed some personnel "were having difficulties," and medical transports were begun, he said.
Eighteen of the soldiers were transported to Womack Army Medical Center, and one was admitted to the intensive care unit, he said.
Humidity levels Friday morning were higher than expected, but "this is odd, out of the norm, to have this many people treated," Abel added.
The expert field medical badge is deemed by the Army as "the utmost challenge to the professional competence and physical endurance of the soldier medic," Fort Bragg officials said in a statement earlier this week.
"It is the most sought-after peacetime award in the Army Medical Department, and while the combat medical badge is the 'portrait of courage' in wartime, the expert field medical badge is undoubtedly the 'portrait of excellence' in the Army all of the time," officials said.
"To wear the EFMB means you passed a grueling series of hands-on-tests on communications, common skill tasks, emergency medical treatment, evacuation of the sick and wounded, litter obstacle course, day/night land navigation courses, comprehensive written test, 12-mile foot march, CPR, physical fitness test, and weapons qualification," the base said.
In June 1965, the Department of the Army established the badge as a special skill award for the recognition of exceptional competence and outstanding performance by field medical personnel.