NHK has found a record of conversations among US Marines who were on the ground during the Battle of Okinawa in the final stages of World War II.

More than 30 hours of unedited audio tape reveals the fierceness of the fighting.

NHK has obtained the tape kept in a conservation center of the US Library of Congress in the eastern state of Virginia.

The recording was made by a Marine in charge of radio correspondence. It was intended to deliver the voices of the troops to the people back home in the US.

This recording got underway in March 1945, just before US forces landed on Okinawa.

The tape, believed to be made shortly after landing, says, "There are some big guns going off now, pounding the hell out of Okinawa." It goes on to say, "From our smallest to the largest guns, they are all opening up in Okinawa."

Sound believed to be captured during battle on the Motobu Peninsula in the northern part of Okinawa's main island says, "That was close. Get away from that recording jeep. Get up here by the hill."

It was a tense moment for the Marines, who were apparently being targeted by Japanese snipers in the forest.

The recording also revealed difficulties faced by Marines in distinguishing Japanese soldiers from civilians. It also depicted the battle over a hill in Naha City called a sugar loaf.

Hosaka Hiroshi, a former professor at the University of the Ryukyus and an expert on the Battle of Okinawa, called the finding an important one that helps testify to the fierceness of the combat there.

He said even specialist researchers like him did not know such recordings of voices of US Marines on the battle ground existed.