More than 70 years after a Japanese submarine slammed two torpedoes into her side and sent the USS Indianapolis to the bottom of the Pacific Ocean, the ship’s wreckage was found by a civilian research team.

On the night of June 29, 1945, coming back from the island of Tinian to Leyte in the Philippines, having just delivered the atomic bomb destined for Hiroshima, the Indianapolis was stalked by a Japanese submarine. The sub fired six torpedoes, two of which struck the U.S. warship. The vessel went down in 12 minutes.

On Aug. 18, the expedition crew of Research Vessel Petrel, owned by Microsoft [MSFT] co-founder and philanthropist Paul G. Allen found the Indianapolis in 18,000 feet of water, resting on the floor of the North Pacific Ocean.

Bow-on view of the USS Indianapolis, taken off the Mare Island Navy Yard, California, 10 July 1945, after her final overhaul. Photograph from the Bureau of Ships Collection in the U.S. National Archives.
Bow-on view of the USS Indianapolis, taken off the Mare Island Navy Yard, California, 10 July 1945, after her final overhaul. Photograph from the Bureau of Ships Collection in the U.S. National Archives.

“To be able to honor the brave men of the USS Indianapolis and their families through the discovery of a ship that played such a significant role during World War II is truly humbling,” Allen said in a prepared statement. “As Americans, we all owe a debt of gratitude to the crew for their courage, persistence and sacrifice in the face of horrendous circumstances. While our search for the rest of the wreckage will continue, I hope everyone connected to this historic ship will feel some measure of closure at this discovery so long in coming.”

The bomb mission was so secret and the vessel sank so fast that no distress signal was sent and much of the lifesaving gear aboard was not deployed.

Of 1,196 men aboard, about 1,000 men went into the water having survived the explosions and subsequent sinking. Only 316 of those men would survive the ensuing four and a half days adrift, during which they formed themselves into tight groups to stay afloat and ward off marauding sharks. At around noon the fifth day after the sinking, a Lockheed PV-1Ventura on routine patrol spotted men in the water and set in motion a rescue operation.

A PBY Catalina float plane found some of the survivors soon after and began to pick them up. The remainder of the survivors were pulled from the water by the USS Cecil B. Doyle, a destroyer escort that responded to the rescue effort.

The 250-foot R/V Petrel was outfitted with state-of-the-art subsea equipment capable of diving to 6,000 meters, or three and a half miles below the surface.

The 16-person expedition team on the R/V Petrel will continue the process of surveying the full site as weather permits and will be conducting a live tour of the wreckage in the next few weeks. The USS Indianapolis remains the property of the U.S. Navy and its location will remain confidential and restricted. The crew of the R/V Petrel has been collaborating with Navy authorities throughout its search operations and continues to work on plans to honor the 22 crew members still alive today and their families.

“Even in the worst defeats and disasters there is valor and sacrifice that deserve to never be forgotten,” said Sam Cox, Director of the Naval History and Heritage Command. “They can serve as inspiration to current and future Sailors enduring situations of mortal peril. There are also lessons learned, and in the case of the Indianapolis, lessons re-learned, that need to be preserved and passed on, so the same mistakes can be prevented, and lives saved.”

Researchers at the Naval History and Heritage Command in 2016 were able to identify a naval landing craft that had recorded a sighting of the Indianapolis the night that it was torpedoed. Using that new information, the research team developed a new position and estimated search, which was still a daunting 600 square miles of open ocean.

Allen-led expeditions have also resulted in the discovery of the Japanese battleship Musashi (March 2015) and the Italian WWII destroyer Artigliere (March 2017). His team was also responsible for retrieving and restoring the ship’s bell from the HMS Hood for presentation to the British Navy in honor of its heroic service.