On July 16, 1945, the heavy cruiser Indianapolis departed the California coast for the Pacific island of Tinian. On board was a heavily guarded top-secret cargo destined to end the war. Only hours before the Indianapolis began her high-speed journey, the first successful atomic detonation had ushered in the nuclear age. The cruiser itself carried vital elements of the atomic bomb that would be dropped on Hiroshima. Even Captain Charles B. McVay III, in command since November 1944, did not know the contents of his mysterious shipment. He had been assured, however, that every hour he cut from travel time would shorten the war. Captain McVay took this admonition seriously, and the vessel made the five-thousand-mile voyage in only ten days.
After delivering her lethal cargo to the American base at Tinian on July 26, the Indianapolis proceeded to Guam and prepared for the final leg of her voyage across the Pacific to the Philippine island of Leyte. There the ship was to complete two weeks of training in preparation for joining Naval Task Force 95 at Okinawa, where plans were under way for the expected invasion of Honshū in November of 1945.