BEIJING — As more than 100,000 Chinese soldiers swarmed over far fewer American Marines and soldiers in subzero temperatures on treacherous terrain in one of the fiercest battles of the Korean War, two United States Navy pilots took off from an aircraft carrier to provide cover for their comrades on the ground.

One of the airmen, Ensign Jesse L. Brown, was the son of an African-American sharecropper from Mississippi. The other, Lt. Thomas J. Hudner Jr., was the son of a white patrician merchant family from Massachusetts.

An hour into the flight, Ensign Brown’s plane was hit by enemy fire, forcing him to crash land on the side of a mountain at Chosin, north of Pyongyang. Lieutenant Hudner brought his plane down nearby and found Ensign Brown, but could not rescue him.

On Monday, nearly 63 years after the Battle of Chosin Reservoir, Mr. Hudner, 88, arrived in Beijing after a 10-day visit to North Korea aimed at finding his friend’s remains....