NEW YORK — Colonel Leo K. Thorsness, one of the most decorated US airmen of the Vietnam War and a belated recipient of the Medal of Honor for his heroism on a mission that took place 11 days before he was shot down and taken prisoner, died Tuesday in Jacksonville, Fla. Colonel Thors-ness, who had been brutalized during his six years of captivity at the notorious North Vietnamese prison known as the Hanoi Hilton, where he was a cellmate of John McCain’s, was 85.

His death was announced by the Congressional Medal of Honor Society, which said he had been treated for cancer. Colonel Thorsness, who lived in St. Augustine, Fla., died at the Mayo Clinic in Jacksonville, WHNT News 19 in Huntsville, Ala., reported. He had been living in Alabama before moving to Florida.

The skies some 40 miles southwest of Hanoi were filled with North Vietnamese MiG fighters, surface-to-air missiles, known as SAMs, and antiaircraft fire on the afternoon of April 19, 1967, when Colonel Thorsness, then a major, carried out his 88th mission for the Air Force piloting an F-105 Thunderchief.

He and his weapons specialist, Captain Harold Johnson, shot down one MiG, damaged another, and struck at least two SAM batteries as they accompanied fighter-bombers attacking a North Vietnamese army barracks.

Although running out of ammunition and low on fuel, Colonel Thorsness hovered in the area to ward off MiGs and shot one down as airmen sought to rescue his wingmen, two F-105 crewmen who had parachuted from their craft when it was struck by enemy fire. They were later captured.

Colonel Thorsness passed up a chance for aerial refueling, instead directing a tanker plane to replenish another fighter whose pilot had become lost in the skies amid the chaos.

He finally headed to the nearest airfield in Thailand, 70 miles to the south.

“I pulled the power back to idle and we just glided in,’’ he told Air Force Magazine in 2005. “We were indicating ‘empty’ when the runway came up just in front of us and we landed a little long. As we climbed out of the cockpit, Harry said something quaint like ‘that’s a full day’s work.’ ’’

Eleven days later, on Colonel Thorsness’ 93rd mission, with only seven remaining to make him eligible to end his tour, a MiG hit his plane with an air-to-air missile. He bailed out with Johnson, suffering severe knee injuries as he ejected, and both were captured.

Colonel Thorsness and Johnson were held captive at the same prison camp, sarcastically labeled the Hanoi Hilton by prisoners, where McCain, later a US senator and presidential candidate, was held. Guards there routinely beat and tortured POWs.

Colonel Thorsness was in captivity when he learned that he had been recommended for the Medal of Honor, for aiding fellow airmen while in great peril on that 88th mission. Word of it came from the officer who had written the recommendation; he had later been shot down and taken to the Hanoi Hilton as well.

But no announcement was made by US military officials until Colonel Thorsness’ return home in March 1973 out of fear that his captors would retaliate with even greater brutality.

He received the medal from President Richard M. Nixon in a White House ceremony Oct. 15, 1973, for “extraordinary heroism, self-sacrifice and personal bravery.’’

He was also awarded two Silver Stars and five Distinguished Flying Crosses for his exploits in the war. Johnson was awarded the Air Force Cross.

In an op-ed article he wrote for The New York Times in September 2008, Colonel Thorsness recalled how McCain, whose Navy plane had been shot down in October 1967, was among his cellmates.

“I still see us sitting on a bed slab in a 6-by-7-foot cell talking about the questions we always talked about: When would the war end? Would we ever be able to catch up with our peers, our families, our faith and our friends?’’

Leo Keith Thorsness was born Feb. 14, 1932, in Walnut Grove, Minn., where his parents had a farm. He enrolled at South Dakota State University in 1950, then enlisted in the Air Force a year later.

In fall 1966, he was assigned to a fighter wing based in Thailand as one of the airmen who became known as Wild Weasels for their prime missions: knocking out SAM batteries, an especially hazardous operation, to protect fighter-bombers during raids.

He could not resume flying after he returned home because of his damaged knees and the injuries he suffered as a prisoner. He retired from the Air Force 10 days later and was promoted to colonel.

While living in South Dakota, he entered politics as a Republican and waged an unsuccessful bid in 1974 to capture the US Senate seat held by George S. McGovern, a staunch opponent of the Vietnam War, who had been defeated by Nixon when the president won a second term two years earlier. McGovern was reelected to a third term.

In a 1978 race to fill a vacant South Dakota seat in the House of Representatives, Colonel Thorsness lost narrowly to Tom Daschle, a future Senate majority leader.

Colonel Thorsness was later director of civil affairs for Litton Industries in Beverly Hills, Calif., then moved to the Seattle area and was a Washington state senator from 1988 to 1992.

He received a bachelor’s degree from the University of Nebraska Omaha in 1964 and a master’s degree in systems management from the University of Southern California while working at Litton.

Colonel Thorsness leaves his wife, Gaylee, their daughter, Dawn, and grandchildren.

McCain issued a statement Wednesday saying Colonel Thorsness had endured “unspeakable pain and suffering because of his steadfast adherence to our code of conduct’’ during his six years in captivity, including a year in solitary confinement, “but Leo never let this experience break his spirit, and inspired the rest of us with his patriotism, perseverance, and hope that we would someday be free.’’

McCain profiled Colonel Thorsness in “13 Soldiers: A Personal History of Americans at War’’ (2014), written with Mark Salter.

McCain wrote that “word had circulated among the POWs’’ that Colonel Thorsness had been recommended for the Medal of Honor, “as had the story of how he earned it.’’

As McCain put it: “Valor like his is hard to keep secret from men who have need of it.’’