By the spring of 1865, a weary, war-torn nation had had enough.

America’s deadliest war was sputtering to a bloody close. Its first president to die at an assassin’s hand had just been murdered and was awaiting burial. Next, the killer was killed.

Then came a tragedy so immense, that it still holds a record today.

It wasn’t supposed to have turned out that way. It should have been the opposite, a Hollywood-style happy ending for men who had suffered—and survived—some of the Civil War’s worst horrors. Yet in an instant, the Disney tale turned into a horror movie.

In 1865, hundreds of steamboats chugged the Mississippi River from Minnesota to New Orleans carrying products and people. It was a busy place then, the quickest way to travel long distances when you were in a hurry.

The men in blue were indeed in a hurry to get home. After all, most of them were Union soldiers recently released from the Andersonville POW camp in Georgia. With the war over, the weakened survivors wanted to put it behind them.

Enter the steamboat, Sultana. She was designed to carry cotton on runs from St Louis to the Big Easy. But money is money, and her owner supplemented his income by ferrying Federal troops up and down the river. When used as a passenger vessel, she was authorized to carry 376 people.

The Sultana was docked at Vicksburg, Miss. when an army officer came looking for Captain James Mason. The officer knew the war had hit Mason’s bottom line hard and that he desperately needed cash to keep his boat in business.

The officer had a problem of his own, too. A temporary holding camp outside town was overrun with liberated soldiers from Andersonville and another POW camp in Alabama. So, he offered a deal.

The army paid $2.75 for each enlisted man and $8 for every officer transported up the river. If Mason would turn a blind eye to the number of men crammed on board, plus give a generous kickback to the officer, the Sultana’s trip upriver would be her most lucrative ever. They shook hands.

When the anchor was weighed and her side paddlewheel began churning on the night of April 24, an estimated 1,960 liberated prisoners, 22 other soldiers, an additional 70 paying travelers, plus a crew of 85 were aboard. That was 2,137 people—on a boat designed to carry 461.

The sight was so unusual when the Sultana docked upriver at Helena, Ark. some 36 hours later, photographer Thomas Bankes rushed to the levy to capture the scene. Photography was cumbersome and time-consuming back then, meaning such an overloaded boat was so extraordinary it was considered worth preserving. The image clearly shows Sultana listing to port from the excess weight. A few hours later she took off again. There had been engine trouble. Worse was to come.

It was slow going, paddling against the ferocious current with a weight the boat was never intended to bear. On top of everything, the Mississippi was at flood stage just then. The boat’s complex steam engine, prone to problems even in ideal conditions, strained to provide power.

She reached Memphis around 7:00 p.m., dropped off some 200 men and 120 tons of sugar freight while taking on several tons of coal, then resumed plodding northward at midnight.

Two hours later, it happened.

There was a massive explosion. A giant fireball lit up the spring night. Bodies and pieces of wreckage flew everywhere.

Survivor Anna Annis recalled, “… my husband, with our child, jumped overboard … I held on to the rudder till I was obliged to let go by the fire.”

Solomon Bogart said, “I jumped overboard among countless numbers of drowning men and made my way to the bank after hard swimming for eight or nine miles.”

We’ll never know the exact number of fatalities. Estimates range from 1,100 to as many as 1,547. Recent research suggests it was likely close to 1,200.

Some people suggested it was an act of late-war sabotage. While many theories about the explosion’s cause abound, it was most likely mechanically related.

Two things are beyond dispute. First, no one was held accountable. Captain Mason died in the blast. The army officer who bribed him was found guilty in a court-martial, but his sentence was later overturned.

Second, it remains the worst disaster in American maritime history. The approximately 1,200 lives lost put it on par with the Titanic’s 1,500 death toll.

So given the magnitude, why don’t we remember it today? Because it happened at the wrong time. It occurred at the end of a month that had already seen more than its share of death. It was finally one tragedy too many. Americans simply wanted to forget.

And forget they did.