Sybil Stockdale is going to be buried Friday at the US Naval Academy at Annapolis, where she’ll rest beside her husband, Vice Admiral James Stockdale. He was one of the greatest heroes in American history — and so was she.

They are a pair to think about in our cynical and feminist age. He led a battered band of brothers to defy a barbaric foe holding them as prisoners of war in the dungeons of Hanoi. For this America would drape him with the Medal of Honor.

On the other side of the world, Sybil Stockdale led an uprising of those prisoners’ wives to spur our own government to fight for them. She represented their cause to the Pentagon, the president, the Congress and envoys of the enemy.

Sybil understood that it would be impossible to support our prisoners (and our GIs) in Vietnam without supporting the war they were fighting. She let no light show between her and America’s government.

Her husband invented the secret code that enabled the prisoners in the “Hanoi Hilton” to tap out the messages to one another that kept their spirits up. She hid within her love letters secret war messages that only he and she could decipher.

After the war, the Stockdales wrote a book called “In Love and War.” It’s a classic American memoir, ranking with the letters that Abigail Adams exchanged with her husband, John, a hero of the Revolution.

The Stockdales had fallen in love while he was at the Naval Academy. After an Army-Navy game, the future admiral asked whether she’d like to go to Annapolis to “look at miniatures” of the academy’s class ring.

“Do you mean what I think you mean?” she asked. Stockdale said he did, and she said it was a grand idea. “Jim had just asked me to marry him,” she would later write, “and I had accepted.”

Stockdale fell into enemy hands in September 1965, after ejecting from his A-4 Skyhawk, which had been disabled by enemy fire over North Vietnam. What he did in the Communist prisons was incredible. Most Medals of Honor are bestowed for acts of a few moments displaying conspicuous courage — charging an enemy machine gun, say, or throwing oneself on an enemy grenade to protect others.

Stockdale’s medal recognized countless acts of valor over a period of more than seven years. He once slashed his brow and beat his own face bloody with a wooden footstool so that he could not be filmed for propaganda.

One day his jailers handed him some letters from Sybil. She’d enclosed a photo of his “mother” bathing in the Pacific. Sybil wrote that his mother had flown to California for an unannounced visit and the chance to go swimming. All she needed, Sybil wrote, was a good soak.

Stockdale was mystified. His mother feared flying, hated unannounced visits and was afraid of the ocean. What would she need with a good soak? Then it dawned on him. He filled his bucket with urine and used it to soak the photograph.

The picture peeled in two, disclosing a hidden message between the sheets that made up the photo. It said that letters dated on odd-numbered days would be on paper containing invisible carbon. He could use that to send back secret messages.

Suddenly Stockdale felt his heart fill with “a secret glow.” The invisible carbon enabled him to begin the transmission of intelligence back to the states — names of prisoners, news of torture and the urgency of targeting the Communist radio station.

At home, Sybil challenged the claim of an anti-war presidential candidate, George McGovern, that he would win the release of the prisoners within 90 days. She called it “incredibly irresponsible.” She grasped that it could only incentivize the Communists to hang tough.

It was during Richard Nixon’s second term that the prisoners were finally released. In 1992, Stockdale himself stood for vice president on Ross Perot’s ticket. He was mocked by the press for introducing himself with the questions “Who am I? Why am I here?”

Yet long after his detractors are lost in the dustbin of history, I once wrote, America will know exactly who James Stockdale was and why he was here — and that he got back here by dint of the woman he’d invited to pick out a miniature three generations ago.

This column first appeared in the New York Post.