On July 30, 1945, the USS Indianapolis was torpedoed by a Japanese submarine and sunk within minutes in shark-infested waters. Only 316 of the 1,196 men on board survived.

Just after midnight on July 30, halfway between Guam and Leyte Gulf, a Japanese sub blasted the Indianapolis. The torpedo sparked an explosion that broke the ship apart, causing it to sink in less than 15 minutes, with about 300 men trapped inside. Another 900 went into the water, where many died from drowning, dehydration, injuries from the explosion or were eaten by sharks. Help did not arrive until four days later, on August 2.

The Indianapolis had just completed a top-secret delivery to Tinian Island on July 26, 1945 – so secret in fact, that even the ship’s captain had no idea what they were carrying.

Captain Charles B. McVay III was ordered to speed highly classified cargo to Tinian Island in the northern Marianas. The shipment consisted of two cylindrical containers and a large crate, accompanied by two Army officers and was to be kept under armed guard at all times.

The cargo contained the instruments of death and instruction, the likes of which the world had never seen. In the containers were key components of the atomic bomb that would be dropped a week later at Hiroshima.

The delivery went according to plan, with the crew none the wiser. The Indianapolis sailed on to Guam, and then on July 28 embarked on a routine voyage to Leyte, Philippines, about 1,200 miles almost due west across the Philippine Sea. The plan was to meet the battleship USS Idaho at Leyte Gulf to prepare for the invasion of Japan.

Captain McVay was told “things were very quiet” by Commodore James Carter, commander of Pacific Fleet’s advance headquarters. So McVay set a direct course, with no destroyer escort.

The ship never made it.

Loel Dene Cox, Seaman Second Class recalled: The big ships like Indianapolis didn’t have sonar and they required some destroyers to be with them. Here we were going from Guam to the Philippines without a destroyer escort. They [both Carter and the Guam routing] assured the captain everything was all right. We left thinking everything was fine. July 30 was a black, dark night.

It was a perfect set-up for the torpedo attack.

The first torpedo slammed into Indy’s starboard bow, killing dozens of men in an instant. Another shattering concussion rocked Indy amidships. Her aviation fuel stores ignited, and a maelstrom of flame and explosions ripped through the ship. Survivors told harrowing stories.

Santos Pena, Seaman First Class said I heard an explosion which knocked me off the ready box, knocking me on the deck. I had no time to get off the deck before I heard the second explosion. I got up as soon as the second explosion and looked forward and found the whole bow was gone… I tried to get communication between sky control and the bridge using sound power phones and the ship’s service phones, but both were out of operation.

The nearly 900 men who made it off the sinking ship alive found themselves swimming in a vast, gooey slab of fuel oil, with searing sun during the day, and the risk of hypothermia at night.

According to Granville Crane, Machinist’s Mate Second Class, Men began drinking salt water so much that they were very delirious. In fact, a lot of them had weapons like knives, and they’d be so crazy, that they’d be fighting amongst themselves and killing one another. And then there’d be others that drank so much [salt water] that they were seeing things. They’d say, “The Indy is down below, and they’re giving out fresh water and food in the galley!” And they’d swim down, and a shark would get them. And you could see the sharks eating your comrade.

By Thursday morning, August 2, when help finally arrived, the dead outnumbered the living. Finally, the surface ships USS Doyle and USS Bassett arrived on the scene to rescue the survivors.

One of the rescuers, Ensign L. Peter Wren, recalled, We get to the survivors and there are these [oil-covered] faces—black hair and faces, round eyes, white teeth. I mean stone black, and it’s midnight. We cut the engines on our boats and said, “Who are you and what ship are you from?” They come back and they still got fight in them, and yell, “Just like a dumbass officer! Asking dumbass questions!”

The U.S. government kept the Indianapolis tragedy secret until August 15 in order to guarantee the disaster wouldn’t overshadow President Harry Truman’s announcement that Japan had surrendered.

In November 1945, Captain Charles McVay, was court-martialed for failing to sail a zigzag course that would have helped the ship evade enemy submarines.. He was the only captain court-martialed for losing a ship during the war. It took 55 years for Congress to finally clear his name in 2000. But it was too late. McVay committed suicide in 1968.