Master Chief Leslie W. Sunday, a US Navy diver, finds himself in custody for being AWOL while watching a familiar face on TV, a person salvaging a nuclear device from the ocean floor. A flashback takes us 25 years earlier to the moment Carl Brashear (Cuba Gooding Jr.) is eager to join the Navy. His impoverished father gifts him a radio and encourages him to be the best. Starting off in the kitchens aboard the USS Hoist, Carl’s impressive swimming skills catch the eye of a captain, leading him to special training for search and rescue despite a few rule breaches.
While diving to salvage a mail chopper wreck, Sunday faces tragedy when a colleague suffers a freak accident. He risks his own life to save him, but in the process, sustains lung damage, effectively ending his diving career. Inspired by Sunday's heroism, Carl vows to pursue becoming a diver himself.
Two years later, Carl joins diving school but struggles socially, as any interaction with him gets his peers expelled by Sunday. Although excelling in physical training, Carl falls short academically. At the library, he meets Jo (Aunjanue Ellis), who recognizes his determination and assists him in his studies. The two eventually marry. Carl's new life also introduces him to Gwen Sunday (Charlize Theron), Leslie's wife, who manipulates Carl to provoke tension with Leslie, to whom she shares an icy relationship.
Leslie's commanding officer, Pappy, pressures him to ensure Carl fails, as he harbors prejudice against a colored man succeeding in the academy. The final test involves assembling a flange underwater from scattered components. Despite the sabotage of his bag, Carl perseveres for 10 hours to deliver a flawless assembly. Sunday defies Pappy's orders to eliminate him.
In a moment of personal turmoil, Sunday lashes out at Lt. Hanks, the man responsible for his discharge post-accident, out of shared resentment. As time goes on, Sunday, while in prison, witnesses Carl's brave retrieval of a nuclear missile. Unfortunately, disaster strikes when the anchor becomes loose, resulting in the loss of Carl's leg, halting his diving dreams.
Years later, Carl opts for amputation and a prosthesis to regain diving eligibility, but Hanks stands as the new head of diving certification, outright denying him. In a twist, Leslie requests four weeks to train Carl and evaluate him in front of the diving committee.
After a month, Carl faces the Naval Personnel, where Hanks introduces a new suit requirement weighing 290 pounds, which entails taking 12 steps on land. With his wife Jo and son in attendance, Carl bravely steps up to the challenge. Chief Sunday approaches to assist Carl in donning the suit, earning Hanks' approval for the trial. With visible discomfort, Carl awkwardly navigates the first few steps until the twelfth, with Chief Sunday urging him on, reminiscent of their earlier training days.
As Hanks acknowledges Carl’s undeniable determination, he confirms that Carl Brashear is hereby reinstated for full diving duty with the Navy, where he continues to serve honorably for another nine years before retirement.
