After delivering the uranium components for the atomic bomb to Tinian, the USS Indianapolis was torpedoed by a Japanese submarine. Because the mission was top secret, the ship was not reported missing when it failed to arrive at its next destination. Of the nearly 1,200 crewmen, about 900 made it into the water. For four days, the survivors drifted in the open ocean, facing dehydration, saltwater poisoning, and constant shark attacks. When they were finally spotted by a patrol plane, only 316 men were left alive. It remains the greatest single loss of life at sea from a single ship in the history of the U.S. Navy.