Updated

Two historians have resolved a decades-old mystery about how many men died when the USS Indianapolis was struck by Japanese torpedoes during World War II.

The Indianapolis Star reports that the number has long varied by one.

Richard Hulver, a historian with the Naval History and Heritage Command, collaborated with historian and filmmaker Sara Vladic on the project.

Nearly 1,200 men were aboard the ship when it was attacked in July 1945. Hulver and Vladic determined that a record-keeping error led to one man's name appearing on some versions of the ship's passenger roster but not on the survivors list.

According to the pair's research, Charles and Ruth Donnor were told their son, Clarence Donnor, was declared missing in action after the tragic voyage. But the couple spoke with their son after the attack and knew he was alive, according to Hulver and Vladic.

The historians found that despite the Donnors informing the Navy of the mistake, the clerical error persisted in some accounts. They also determined that Clarence Donnor didn't sail on the USS Indianapolis because of a last-minute change.

Hulver and Vladic determined the final crew list was corrected to show 1,195 men were on board, but that the number of men killed was 879, not 880.

"To an outside observer, this small casualty discrepancy might seem insignificant," the historians wrote in their report . "To survivors, descendants, friends and the Navy, it is not. ... This entire event shows the inherent difficulties in accounting for casualties in the fog of war."

Hulver and Vladic said their work will help set the record straight for posterity.

Their report was published in a recent issue of the U.S. Naval Institute's Proceedings Today.

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Information from: The Indianapolis Star, http://www.indystar.com