On their first day of training, all aspiring officers in US Navy Officer Candidate School must endure a punishing gauntlet known as "First Tuesday," an intense event that tests them mentally and physically in the span of just under two hours.

Business Insider's chief video correspondent Graham Flanagan went inside "First Tuesday" at Navy OCS in Newport, Rhode Island as 126 candidates began their journey toward earning their commissions as Naval officers.

Led by a US Marine Corps drill instructor, the event sets the tone for the 13-week training course, potentially weeding out anyone having second thoughts.

Peter Rhee is a Navy trauma surgeon who served 24 years in the US military. He operated in several active war zones, including Iraq and Afghanistan.

Peter Rhee speaks to Business Insider about treating bullet wounds, battlefield trauma surgery conditions, AI-powered medical technology, and military medical training

He also discusses his role treating Rep. Gabby Giffords after she was shot in an attempted assassination in 2011 in Arizona.

He is the author of "Trauma Red: The Making of a Surgeon in War and in America's Cities."