The last combat mission of World War II began Aug. 15, 1945, when fighter pilot Jerry Yellin and his wingman, 19-year-old Philip Schlamberg, took off from Iwo Jima to attack airfields near Nagoya, Japan.

The war seemed all but over. Germany had surrendered in May, and much of Hiroshima and Nagasaki were in ruins, decimated by atomic bombs dropped the previous week. If Mr. Yellin heard a code word — “Utah” — Japan’s rumored surrender had occurred, and he was to cancel his mission and return to Iwo Jima, a rocky island that he had helped secure months earlier and that offered a base for American bombers headed north to Japan.

Later that day, on what was still Aug. 14 in the United States, Emperor Hirohito announced Japan’s surrender. For some reason, however, Mr. Yellin and Schlamberg never got the message.

Taking on antiaircraft fire in their P-51 Mustangs, they strafed their targets and headed home, passing through a thick bank of clouds. Schlamberg, who had previously admitted a sense of foreboding to Mr. Yellin, saying, “If we go on this mission, I’m not coming back,” never emerged from the haze.

Disappearing from Mr. Yellin’s wing, he was presumed dead and considered one of the last Americans to be killed in combat during World War II.

Mr. Yellin in 2015. (Lightfinder Public Relations)

Mr. Yellin, who landed on Iwo Jima to discover that the war had ended three hours earlier, and who later became an outspoken advocate of veterans with post-traumatic stress disorder, died Dec. 21 at his son Steven Yellin’s home in Orlando. He was 93 and had lung cancer, his son said.

For Mr. Yellin, the war was a hellish necessity, essential for halting the spread of Nazism and Japanese aggression. But he also spoke forthrightly about its costs, including the mental anguish over memories of combat that nearly led him to suicide. He recalled with particular horror the experience of landing on war-torn Iwo Jima for the first time, where “there wasn’t a blade of grass and there were 28,000 bodies rotting in the sun.”

“The sights and the sounds and the smells of dead bodies and the sights of Japanese being bulldozed into mass graves absolutely never went away,” he told the Washington Times in August.

Mr. Yellin, a captain in the 78th Fighter Squadron of the Army Air Forces, counted 16 downed pilots in his unit during the war, including Schlamberg. For years afterward, he struggled to keep a steady job, moving a dozen times in the United States and Israel (where he settled, at one point, partly in protest of the Vietnam War).

He eventually found solace through Transcendental Meditation, a twice-daily technique of silent concentration that his wife introduced him to in 1975 after she saw the practice’s originator, Maharishi Mahesh Yogi, on “The Merv Griffin Show.”

Mr. Yellin soon began speaking to other veterans who struggled to adapt to civilian life, and in 2010 he co-founded Operation Warrior Wellness, a division of the David Lynch Foundation that helps veterans learn Transcendental Meditation. He said he was inspired to start the group after a friend and Army veteran killed himself that year. Mr. Yellin received support in promotional videos by actress Scarlett Johansson, a grandniece of Schlamberg.

“The feeling that one has when a buddy dies? You just can’t emulate that. We have a burden civilians will never understand,” Mr. Yellin told The Washington Post earlier this month, shortly after the release of “The Last Fighter Pilot,” an account of his World War II service written with Don Brown.