Shark attacks have been in the news a lot this summer, with several attacks happening much farther north than they normally do, and one broadcast on live TV. And though shark attacks are incredibly rare, they remain a subject of genuine terror. We don't like to think about people being anywhere but at the very top of the food chain.

Today is the 70th anniversary of an event that led to what is considered the worst shark attack in history: the bombing and rapid sinking of the USS Indianapolis on July 30, 1945. To mark the event, National Geographic spoke to more than a dozen survivors of the doomed warship in a new video.

The tale they tell is horrific. (It's one that many people first heard in a famous, and partially accurate, monologue by Captain Quint in Jaws.) After delivering enriched uranium and components for Little Boy, the atomic bomb that destroyed Hiroshima about a week later, to a naval base on the Northern Mariana island of Tinian, the Indianapolis was en route from Guam to the Philippines when it was hit by two Japanese torpedoes. In just 12 minutes the warship sank, taking about 300 of the ship's 1196 crewmen down with it.

The rest found themselves in life jackets bobbing in the ocean. At first, the survivors stayed calm; after all, the ship was expected in the Philippines. "They know we're coming. No problem," survivor Vic Bucket remembers thinking. "We just have to sit it out a little bit."

Soon, exposure, dehydration, salt-water poisoning, and hallucinations began to take their toll. "I'd seen a lot of guys just crack—drink the water, or give up, or they'd swim off to imaginary islands," recalls survivor Dick Thelan.

The sharks arrived by sunrise of the first day. Over the next several days, the crewmen's movement and blood drew ever-increasing numbers of what were probably oceanic whitetip sharks, which dismembered or killed one man after another.

Finally, four days after the Indianapolis went down, a pilot spotted the survivors. Though rescue operations began within hours, in the end, only 317 crewmen survived. Estimates vary widely, but as many as 150 people may have been killed by sharks.