On the afternoon of Feb. 28, 1844, President John Tyler and about 400 guests were steaming down the Potomac River on the new warship USS Princeton, enjoying cocktails and music, when the world’s biggest naval gun, the “Peacemaker,” exploded onboard. It came close to costing the nation its leader.

Instead the accident had a different outcome: It led Tyler to become the first president to marry while in office.

Tyler, who hoped to run for a full term in the presidential election that fall, saw the cruise as a way to help mend political fences. The former vice president had succeeded Whig President William Henry Harrison, who died on April 4, 1841, after just a month in office. Tyler, a former Democrat, vetoed so many bills passed by the Whig Congress that the Whigs kicked him out of the party. The Democrats also spurned him. To make matters worse, in 1842, his wife of 29 years, Letitia, died.

To boost U.S. naval power and his own status, Tyler backed development of the USS Princeton under Capt. Robert Stockton. The 164-foot-long warship featured a revolutionary propulsion system, with screw propellers powered by an engine placed under the ship to protect it from enemy fire.

To show off the new ship, Stockton arranged a cruise for the president and Washington VIPs. Guests included former first lady Dolley Madison and top government officials led by two Cabinet members, Secretary of State Abel Upshur and Navy Secretary Thomas Gilmer — who, like Tyler, was a Virginia enslaver.

Also onboard was wealthy Long Island lawyer David Gardiner, with his two daughters. The 53-year-old Tyler was courting one of the daughters, 23-year-old Julia.

The guests arrived at the Alexandria, Va., dock about 11 a.m. on a sunny day. As Stockton greeted the arrivals in his dress uniform, on deck a band played “The Star Spangled Banner.” The Princeton steamed down the Potomac River toward George Washington’s old home at Mount Vernon. Stockton fired the Peacemaker twice, each time a cannon ball “striking the water and rebounding five or six times till the eye would no longer follow its progress,” a New York Herald reporter wrote.

On the return trip, the guests then went below decks for food and numerous toasts. When the ship was about 20 minutes from Alexandria, Navy Secretary Gilmer agreed to fire the Peacemaker again in honor of Washington. Many of the men and some of the women headed up on deck.

“At this moment, Mr. Upshur had his hand on the president’s arm and said, ‘Come Mr. Tyler, let’s go up and see the big gun fired,’ “ a correspondent for the New York Sun reported. Tyler was heading up the steps when his son-in-law began to sing a song about 1776. The president called to Upshur, “No, by George, Upshur, I must stay to hear that song ... it’s an old favorite of mine. You go up, and I’ll join you shortly.”

As the singer finished his song, a loud noise rocked the ship. The guests below cheered the firing of the Peacemaker. Then a sailor, his face covered with black powder, came running down the steps and told Tyler several people had been killed on deck.

The president “rushed up on deck, and when he saw the dead bodies of Upshur and Gilmer, he wept bitterly,” the New York Sun reported. They had been blown to pieces when the Peacemaker exploded upon firing, sending hot metal in all directions. Gilmer had been appointed to his Cabinet post just 10 days before. Four others also were dead, including David Gardiner and Tyler’s enslaved valet, Henry Armistead. Gardiner’s watch had stopped at 4:06 p.m.

If Tyler had gone on deck, he surely would have been standing with the two dead Cabinet members. “It is incredible that a jolly military song should have delivered this man from crippling injury or death,” one bystander said, according to Kate Havelin in her book “John Tyler.”

When Julia Gardiner arrived on deck and heard her father was dead, she fainted. Julia told an interviewer years later that Tyler picked her up and carried her across a gangplank to a rescue boat. She said she awoke and tried to shake loose, “I almost knocked us both off the gangplank. I did not know at the time that it was the President whose life I almost consigned to the water.”

After the catastrophe, Tyler came to a decision. During a carriage ride with his friend Sen. Henry Wise, D-Va., he said he was determined to marry Julia. When Wise suggested the president might be a tad old for such a young wife, Tyler replied with a chuckle: “Pooh. Why, my dear sir, I am just full in my prime.”

Julia had resisted Tyler’s previous marriage proposals, but the tragedy changed her mind. “After I lost my father, I felt differently toward the president. He seemed to fill the place and to be more agreeable in every way than any younger man ever was or could be,” she said later.

On June 26, 1844, Tyler and Julia married in a private ceremony at the Church of the Ascension on Fifth Avenue in New York City. Tyler was 54 and Julia was 24. The age difference raised eyebrows. Former Ppresident John Quincy Adams wrote in his diary that Tyler was “performing with a young girl from New York the old fable of January and May.”

Since Tyler, two other presidents have married while in office. In 1886, bachelor Grover Cleveland became the only president to get married in the White House itself. Like Tyler, the 49-year-old Cleveland wed a much younger woman, 21-year-old Frances Folsom, the daughter of a family friend who had been killed in a carriage accident 10 years before. In 1915, 58-year-old widower Woodrow Wilson married 43-year-old Edith Bolling Galt.

Tyler didn’t run in the 1844 election, and James K. Polk took office in 1845. Tyler and his family moved to Charles City County, Va., near his boyhood home. Since the Whig Party considered him an outlaw like Robin Hood, he named his new slave plantation Sherwood Forest. When the Civil War began, Tyler sided with the South. He was on his way to join the Confederate Congress when he died in Richmond on Jan. 18, 1862, at age 71.

Tyler holds a record unlikely to be broken: most children by a president. He had 15 children, eight with Letitia and seven with Julia. When he married Julia, he apparently really was just full in his prime.

Ronald G. Shafer is a former editor at the Wall Street Journal and the author of “The Carnival Campaign: How The Rollicking 1840 Campaign of Tippecanoe and Tyler Too Changed Presidential Elections Forever.”