Every summer, nearly 8,000 college students from across the country head to Fort Knox, Kentucky, for Cadet Summer Training — the largest annual training event for the US Army.

The program is divided into two camps: Basic Camp, a 30-day introduction for students exploring ROTC, and Advanced Camp, a grueling 36-day assessment that determines whether contracted cadets can graduate and commission as Army officers.

During their time at Cadet Summer Training, the cadets participate in field training exercises, obstacle course, gas-chamber immersion, 60-foot rappels, and more.

Business Insider spent four days inside Fort Knox observing both camps to see firsthand what it takes to complete these training events — and to hear from cadets about why they chose this path of military service.