Men of Honor

Carl Brashear (Gooding, Jr.) leaves his native Kentucky and the life of a sharecropper in 1948 by joining the United States Navy. As a crew member of the salvage ship USS Hoist, where he is assigned to the galley, he is inspired by the bravery of one of the divers, Master Chief Petty Officer Leslie William "Billy" Sunday (De Niro). He is determined to overcome racism and become the first black American Navy diver, even proclaiming that he will become a master diver. He eventually is selected to attend Diving and Salvage School in Bayonne, New Jersey, where he arrives as a boatswain's mate second class. He finds that Master Chief Sunday is the leading chief petty officer and head instructor, who is under orders from the school's eccentric, bigoted commanding officer to ensure that Brashear fails.
Brashear struggles to overcome his educational shortcomings, a result of his leaving school in the 7th grade in order to work on his family's failing farm. He receives educational assistance from his future wife, a medical student who works part-time in the Harlem (New York City) Public Library. Brashear proves himself as a diver by rescuing a fellow student whose dive buddy abandons him during a salvage evaluation. Unfortunately, due to the racism of the commanding officer (Hal Holbrook), the student who fled in the face of danger is awarded a medal for Brashear's heroic actions. Likewise, during an underwater assembling task where each student has to assemble a flange underwater using a bag of tools, Brashear's bag is cut open. Brashear nevertheless finishes the assembly and graduates from diving school, earning the quiet and suppressed admiration of Master Chief Sunday and his fellow divers. Master Chief Sunday is later demoted to senior chief by the commanding officer for standing up for Brashear and allowing him to pass.
The paths and careers of Brashear and Sunday sharply diverge. Brashear rises quickly through the ranks, even becoming a national hero in the 1966 Palomares B-52 crash (Spain) for recovering a missing atomic bomb and for saving the life of Navy crew. Sunday continually loses his composure around officers who disrespect his accomplishments, until he is finally demoted to chief petty officer and relegated to menial duties. He becomes a brooding alcoholic displeased with his rank, relatively low for someone with so many years of service.
The two eventually meet again after Brashear's left leg was so mangled by the atomic bomb incident that he feels that his only chance to return to active duty and a relatively normal life is for it to be amputated and replaced with a prosthesis. Until this time, no Navy man had ever returned to full active duty with a prosthetic limb. Sunday again trains Brashear and aids him in his fight against the US Navy bureaucracy and an antagonistic Navy captain (a former lieutenant and their former Hoist executive officer) in order to return to full active duty and fulfill his dream of becoming a master diver. They succeed in getting Brashear reinstated.
In the epilogue, it is noted that two years later Brashear becomes a master diver. It is added that he does not retire from the Navy for another nine years.

Question: Who continually loses his composure around officers?
Answer: Sunday; Sunday