For seven weeks straight, BUD/S student will undergo constant physical conditioning. During this first phase of training, each individual is observed carefully and independently. The purpose of this is to ensure that someone is fit both physically and mentally before he’s put in situations where he could hurt others.

Each week, and for the rest of one’s career, these men are expected to do more, go faster, swim farther, and get stronger. “The only easy day is yesterday” is a mantra adhered to from this point on.

Weekly, the men of First Phase must pass an increasingly demanding timed run, a timed obstacle course, and a two-mile timed ocean swim. As a form of test and evaluation, this may sound simple enough, but it’s important to keep in mind that these men are also undergoing upwards of 10 hours of physical training a day. Staying healthy and uninjured is as much a test as any timed evolution.

It is in the fourth week of training that Hell Week occurs. This is a physically and unfathomably mentally demanding five-and-a-half-day evolution created by LT. Draper Kauffman of the Naval Combat Demolition Units (NCDUs). Every day consists of no less than 20 hours of physical training and a plethora of mental challenges. Within this week, each man will have run more than 200 miles with most of the miles being run with a boat pounding on his head.

Though Hell Week is a ‘team evolution’ in its structure—you’re always with your boat crew—it’s very much an individual accomplishment, as each man is under the constant watch of the instructors as they work to weed out those who are not cut out for such punishing conditions.