Civilian researchers have located the wreck of the USS Indianapolis, the World War II heavy cruiser that played a key role in the atomic bombing of Hiroshima before being struck by Japanese torpedoes.

The expedition crew of Research Vessel Petrel, which is owned by Microsoft co-founder Paul Allen, said it located the wreckage of the Indianapolis on the floor of the North Pacific Ocean, more than 5,500 metres below the surface.

Researchers deployed the autonomous underwater vessel to investigate information that surfaced in 2016 indicating the vessel may have sunk to the west of its original presumed position.

The expedition searched a 1,550-square-kilometre portion of the Pacific Ocean that eventually led to the discovery of the sunken warship.

Crews were able to identify the ship based on its markings.

Some fragments recovered from the wreckage made identification of the ship possible. ( Supplied: Paul G Allen )

The Indianapolis delivered key components of what would become the "Little Boy" atomic bomb to the island of Tinian, the take-off point for the bomber Enola Gay's mission to Hiroshima in August 1945.

Its sinking remains the US Navy's single worst loss at sea.

Headlines from the day the USS Indianapolis sank during WWII ( Chicago Daily Tribune )

The heavy cruiser, with 1,196 sailors and marines on board, was sailing the Philippine Sea between Guam and Leyte Gulf when two torpedoes from a Japanese submarine struck just after midnight on July 30, 1945.

Within 12 minutes, the ship had sunk and 300 people were dead.

Survivors were left in the water, most of them with only life jackets.

There was no time to send a distress signal, and four days passed before a bomber on routine patrol happened to spot the survivors in the water.

By the time rescuers arrived, a combination of exposure, dehydration, drowning and constant shark attacks had left only a quarter of the ship's original number alive.

An image shot from a remotely operated vehicle shows the wreckage of the USS Indianapolis. ( Supplied: Paul G Allen )

The fate of the ship and its crew — nearly 900 were killed, and just 316 survived — was one of the Pacific war's more horrible and fascinating tales.

The navy news release issued on Saturday said a key to finding the Indianapolis came in 2016 when a historian with the Naval History and Heritage Command determined a new search area.

His research identified a naval landing craft that had recorded a sighting of the Indianapolis the day before it sank, helping the research team to develop a new search area.

The US Navy said the R/V Petrel team's work had been compliant with US law regarding a sunken warship as a military grave not to be disturbed.

The craft remained the property of the navy and its location both confidential and restricted, it said.

"To be able to honour the brave men of the USS Indianapolis and their families through the discovery of a ship that played such an important ole during WWII is truly humbling," Mr Allen said of the new discovery.

The WWII cruiser USS Indianapolis (CA 35) is seen at Pearl Harbour in 1937. ( Reuters: US Navy )

AP