http://www.npr.org/2015/07/26/425904134/cost-of-war-veterans-remember-uss-indianapolis-shark-attacks
A Japanese submarine surfaced not far away, saw the silhouette of the ship on the horizon and began tracking it.
Torpedoes were fired and the ship sank in just 12 minutes.
There hadn't been time to get enough life boats into the water, so the survivors clung to life jackets, makeshift rafts and debris, thinking they'd be rescued within a few hours. But after two and a half days in the water, they realized help wasn't coming.And then things got even worse. Hundreds of sharks had been feeding on those killed in the explosion. But now they turned their attention to the survivors. Thelen saw people get taken by the sharks.
About 900 men survived the torpedo attack after the ship sank. By the time of the rescue only 321 survivors were pulled from the water.
"Years ago, I wouldn't be talking about it to you or anybody else. I wouldn't talk about it for years," Thelen says.
Captain McVay, Captain of the Indianapolis, never got over losing all his men. Feeling sorry about how the Navy was treating the submarine captain after the war, McVay gave his wife $100 and had her take him shopping for food and presents for his family back in Japan. Years later McVay committed suicide with his service pistol, with a little plastic sailor clutched in his hand.
The Navy, humiliated by this fiasco, tried to indict the submarine captain for a war crime! On the stand, the captain said that the U.S. Navy plowed the sea as if they were on streets. The captain said he simply positioned his sub athwart one and just waited. Didn't have to wait too long. Sure enough, there came the Indianapolis.
See also Quint's Indianapolis speech from the movie Jaws: