Before they can begin their training to become Air Assault-qualified, all students at the Sabalauski Air Assault School must survive "day zero," a physically and mentally grueling test that marks the beginning of what's known as the Army's "10 toughest days." Beginning before sunrise, day zero consists of a detailed inspection of the students' gear, a 2-mile run and culminates with an intimidating obstacle course featuring two major events that all students must conquer — otherwise they are dropped from training before phase one begins. On a scorching day in June where the heat index rose to over 100 degrees, Insider followed two students to find out if they have what it takes to survive day zero and move on to day one of Air Assault School.

Located inside the Fort Campbell Army installation on the Tennessee-Kentucky border, the Air Assault School is where students train to insert themselves and equipment into combat using helicopters.